Patent Publication Number: US-2011070811-A1

Title: Point of use recycling system for cmp slurry

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/211,156 (Attorney Docket No. 14199L01), filed Mar. 25, 2009, U.S. Provisional Patent Application Ser. No. 61/163,451 (Attorney Docket No. 14199L02), filed Mar. 26, 2009, U.S. Provisional Patent Application Ser. No. 61/170,413 (Attorney Docket No. 14199L03), filed Apr. 17, 2009, and U.S. Provisional Patent Application Ser. No. 61/185,424 (Attorney Docket No. 14199L04), filed Jun. 9, 2009. All the aforementioned patent applications are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to apparatus and method for recycling polishing slurry and rinse water in a chemical mechanical polishing (CMP) system. 
     2. Background 
     Due to the high cost of CMP polishing slurry recycling CMP polishing slurry from CMP process has been the subject of numerous studies. Polishing slurries are generally comprises about 3% to about 30% solid particles suspended in water. Polishing slurry generally accounts about 50% of CMP cost. 
     However, recycling and reuse of CMP polishing slurries for use in semiconductor processing faces significant challenges. During CMP processing, particle concentration, particle size, particle homogeneity have profound effect in removal rate and defect reduction, therefore, must be carefully controlled. However, these factors are difficult to achieve in recycled polishing slurry because some particles are crushed and some of the particles agglomerate during polishing, and particles of removed materials enter into the polishing slurry. 
     Additionally, recycling rinsing water is also of interest to reduce cost of ownership. However, there is concern that recycled water is not satisfactory to perform multiple rinses post polishing. 
     Therefore, there is a need for apparatus and method for recycling polishing slurry and rinse water in a chemical mechanical polishing system. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to apparatus and method for recycling both polishing slurry and rinse water from CMP processes. 
     One embodiment of the present invention provides an apparatus for recycling comprising a first filtration unit, wherein the first filtration unit comprises an inlet configured to receive one or more of used polishing slurry, rinsing fluid, such as water, glycol or others, and polishing waste, a water outlet configured to output a first filtered stream for water recycling, and a chemical outlet configured to output a second stream for recycling polishing slurry, a second filtration unit, wherein the second filtration unit comprises an inlet connected with the chemical outlet of the first filtration unit, a product outlet configured to output a stream of recycled polishing slurry, and a water outlet configured to output another filtered stream for water recycling, and an optional UV (ultra violet) unit, wherein the UV unit comprises an inlet connected with the water outlet of the first and/or filtration unit, and an outlet configured to output a stream of UV treated fluid. 
     Another embodiment of the present invention provides a method for recycling polishing fluid, comprising filtering one or more of used polishing slurry, rinsing fluid and polishing waste through a first filtration unit to generate a water stream and a suspension stream, filtering the suspension stream through a second filtration unit to separate a stream of reusable polishing slurry from a water stream, flowing the stream of reusable polishing slurry to a polishing slurry source for a polishing station, recycling the water stream, and flowing the recycled water stream to a recycled water source. 
     Yet another embodiment of the present invention provides a chemical mechanical polishing system comprising one or more polishing stations, a polishing slurry unit configured to provide polishing slurry to the one or more polishing stations, a rinse water unit configured to provide rinse water to the one or more polishing stations, and a recycling unit configured to recycle polishing slurry and rinse water, wherein the recycling unit comprises a first filtration unit, wherein the first filtration unit comprises an inlet configured to receive a mixture of used polishing slurry, rinsing fluid, and polishing waste from the one or more polishing stations, a water outlet configured to output a first filtered stream for water recycling, and a chemical outlet configured to output a second stream for recycling polishing slurry, a second filtration unit, wherein the second filtration unit comprises an inlet connected with the chemical outlet of the first filtration unit, a product outlet configured to output a stream of recycled polishing slurry to the polishing slurry unit, and a water outlet, to output another filtered stream for water recycling, an optional UV (ultra violet) unit, wherein the UV unit comprises an inlet connected with the water outlet of the first and/or second filtration unit, and an outlet configured to output a stream of UV treated water, and a treatment unit configured to purify the UV treated water by removing organic compounds, and or to kill bacteria wherein the treatment unit comprises, an inlet connected to the outlet of the UV unit, and an outlet configured to output a stream of purified water to the rinse water unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is a schematic chart of a polishing system having a recycling unit in accordance with one embodiment of the present invention. 
         FIG. 2A  is a schematic chart of a polishing system having a recycling unit in accordance with one embodiment of the present invention. 
         FIG. 2B  is a schematic chart of a polishing system having a recycling unit in accordance and a centrifugal separator with one embodiment of the present invention. 
         FIG. 2C  is a schematic chart of a polishing system having a recycling unit in accordance and a centrifugal separator with one embodiment of the present invention. 
         FIG. 2D  is a schematic chart of a polishing system having a diverter valve and a recycling unit in accordance with one embodiment of the present invention. 
         FIG. 3  is a schematic chart of a polishing station having a dedicated recycled slurry source in accordance with another embodiment of the present invention. 
         FIG. 4  is a schematic chart of a polishing station having a dedicated recycled rinse water source in accordance with another embodiment of the present invention. 
         FIG. 5  is a schematic chart of a polishing system having multiple polishing stations and a recycling unit in accordance with another embodiment of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention generally relate to apparatus and method for recycling slurry and liquid from various processes that use slurry, such as chemical mechanical polishing, or wire saw cutting applications. 
     Embodiment of the present invention provides apparatus and method for recycling polishing slurry and rinse water discharged from a polishing station. The discharge generally comprises one or more of used polishing slurry, debris from planarized or wire cut surface, rinsing fluid, and particles of removed and pad material. One embodiment of the present invention provides a recycling unit that receives waste mixture and outputs recycled water and recycled polishing slurry. In one embodiment, the recycling unit comprises four filtration/treatment units. A first filtration unit is configured to separate the mixture into a water stream which mainly includes large particles and a concentrate stream which includes solids. The concentration stream then goes through a second filtration unit for further filtration before going back as recycled slurry. Before going back as recycled slurry, a fourth filtration step could be implemented as an option for safety purpose. The stream of water then goes through a third treatment unit to be further purified including optional deionization. 
     Depth filtration, centrifugal separation, microfiltration, nanofiltration, and ultrafiltration may be used alone or in combination in the filtration/treatment units. In one embodiment, magnetically levitated pumps are used in the filtration/treatment units to apply a pressure without deleteriously impacting in the nature of the polishing slurry. 
     In one embodiment, a centrifugal separation unit is used to remove large particles, agglomerates, and/or polymeric particles. The centrifugal separation unit may be positioned before or after a filtration unit. 
     The recycling unit may be configured to recycle polishing slurries from various CMP processes, such as polishing of copper, tungsten, silicon oxides, single crystalline silicon, polycrystalline silicon, or from wire saw applications. 
     Embodiments of the present invention also relate to using centrifugal pumps, such as magnetically levitated pumps, in pumping, mixing, and metering to reduce and prevent agglomeration of particles in the CMP polishing slurry and to reduce particle contamination. In one embodiment, particle agglomeration may be reduced by controlling the amount of sheer when pumping, mixing and metering. 
       FIG. 1  is a schematic chart of a polishing system  100  having a recycling unit  104  in accordance with one embodiment of the present invention. The polishing system  100  may be configured to planarize substrates comprising variety of materials, such as polycrystalline silicon, single crystalline silicon, oxides, tungsten, aluminum, copper, or combinations of different materials. In one embodiment, the polishing system  100  may be used to prepare a polycrystalline silicon substrate for solar panel fabrication. 
     The polishing system  100  comprises a polishing station  101  wherein substrates are polished by a polishing slurry with the assistance of relative motion between the substrate being processed and a polishing pad. The polishing slurry is usually sprayed on the substrate or the polishing pad during polishing. After polishing, one or more rinses of the substrate are carried out by spraying deionized water. 
     The polishing system  100  further comprises a polishing slurry source  102  configured to supply polishing slurry to the polishing station  101 . In one embodiment, the polishing slurry source  102  may comprise one or more slurry tanks configured to store virgin polishing slurry, and/or recycled polishing slurry therein and one or more pumps configured to supply polishing slurry in the tanks to the polishing station  101 . In one embodiment, the pumps may be centrifugal pumps, such as magnetically levitated pumps, configured to provide real time rheology measurements and torque requirements to a system controller. 
     In another embodiment, the polishing slurry source  102  may comprise a slurry generator configured to manufacturing polishing slurry in-situ. The slurry generator assures “fresh” polishing slurry and avoids settling or other aging problems that associated with pre-made polishing slurry. In one embodiment, the slurry generator may be connected to a small local slurry tank to assure steady flow of slurry during processing. 
     The polishing system  100  further comprises a rinse water source  103  configured to supply rinse water to the polishing station  101  for rinsing of the substrates and/or the polishing station  101 . The rinse water source  103  may be configured to supply ultra purified water to the polishing station  101 . 
     In one embodiment, the polishing system  101  may have a tank  119  connected downstream to the polishing station  101  and configured to receive used polishing slurry and used rinse fluid, such as water, glycol or others. In one embodiment, the tank  119  may be coupled to multiple polishing stations and configured to collect mixtures of used polishing slurry and rinsing water from multiple polishing stations. 
     The polishing system  100  further comprises a recycling unit  104  configured to receive the mixture from the tank  119  and to generate reusable polishing slurry, reusable rinse water or both from the mixture in the tank  119 . In another embodiment, the recycling unit  104  may be directly connected to the polishing station  101 . 
     The recycling unit  104  comprises a first filtration unit  150  configured to split received mixture into a water stream with chemicals and particles removed and a concentration stream comprising the majority of chemicals and particles. The first filtration unit  150  may also have a waste outlet that provides an exit for waste, such as large particles. The concentration stream is directed to a second filtration unit  160  to obtain reusable polishing slurry. The water stream is directed to an optional sanitization unit  180  and a treatment unit  170  to obtain reusable clean water. 
     The first filtration unit  150  may comprise a suitable filtering media for depth filtration and/or surface filtration. In one embodiment, the first filtration unit  150  comprises one or more membranes or other filtration units configured to remove particles of different sizes. In one embodiment, the membranes or other filtration units may be microfiltration membrane, nanofiltration membrane, or ultrafiltration membrane. 
     In one embodiment, the first filtration unit  150  may be a cross flow filtration unit. The water stream is the permeate stream that permeates all the one or more membranes and the concentration stream is the reject stream from one of the membranes. In another embodiment, the first filtration unit  150  is a dead-end filtration unit having two or more membranes or other optional filtration technologies, and the water stream is the permeate stream that permeates all the two or more separators. This dead-end filtration unit can optionally utilize a back flush regeneration to clean the membrane surface. The first filtration unit  150  removes particles that are too large for polishing slurry from the concentration stream. 
     The second filtration unit  160  is connected downstream to the first filtration  150  to receive the concentration stream. The second filtration unit  160  is configured to stabilize particle size distribution in the output stream. In one embodiment, the second filtration unit  160  is configured to remove both large particles and small particles from the stream to obtain qualifying abrasive particle size for the stream to be reusable. In one embodiment, the second filtration unit  160  comprises a membrane or other filtering media and a pump configured to pressure the concentration stream through the membrane. The pump may be a magnetically levitated pump that imposes minimal destruction to the abrasive particles in the polishing slurry. The second filtration unit  160  may be cleaned by backward flush to remove waste and surplus water. The water may be exit the second filtration unit  160  through a waste output  165  or will be fed to the treatment unit  170 . In one embodiment, the waste may be about 10% to about 15% of feed stream. The concentrate stream from the second filtration unit  160  goes back to polishing from a slurry output  164 . 
     In one embodiment, the second filtration unit  160  further comprises a dosing unit  167  configured for keeping the abrasive slurries stabilized during processing in the second filtration unit  160 . The dosing unit  167  may provide an additional stream of conditioning chemicals, such as KOH or NH 4 OH  167  to the second filtration unit  160  either before, during or after filtration. 
     The stream from the slurry output  164  may be directed back to a local polishing slurry tank of the polishing station  101  or to combine with virgin polishing slurry in the polishing slurry source  102 . In one embodiment, rinse water or additional chemical, particles may be blended with the slurry output  164  to obtain desired concentration of a polishing slurry for reuse. 
     In one embodiment, the slurry out of the second filtration unit may be filtered with a polishing filtration unit  190  before directed back to a local polishing slurry tank of the polishing station  101  or to combine with virgin polishing slurry in the polishing slurry source  102 . 
     The sanitization unit  180  is optional. In one embodiment, the sanitation unit  180  is configured to remove organic species from the fluid flowing therethrough, such as the water stream from the first filtration unit  150  and/or the water stream from the second filtration unit  160 . In one embodiment, the sanitization unit  180  may be an ultra violet (UV) unit configured to oxidize the organic species in the water stream. In another embodiment, the sanitization unit  180  is configured to reduce and control bacteria counts. 
     In one embodiment, the sanitized water stream out of the sanitization unit  180  is directly flown back to the polishing station  101  for rinsing or other function. The sanitized water stream may be used in a first rinse, which has low requirement for the purity of the rinse water. 
     The treatment unit  170  is configured to purify and/or deionize the water stream. In one embodiment, the treatment unit  170  may comprise a reverse osmosis membrane for a reverse osmosis filtration. In another embodiment, the treatment unit  170  may comprise an ion-exchange resin, which may be continuously regenerated, to deionize the water stream. In another embodiment, the treatment unit  170  may comprise both a reverse osmosis membrane and an ion-exchange resin. The output stream from the treatment unit  170  results in ultra purified water. The rejected stream from the treatment unit  170  exits the recycling unit  104  as waste water. In one embodiment, the waste water is between about 5% to about 20% of feed stream. The purified water from the treatment unit  170  may be sent back to directly to the polishing station  101  or to mix with virgin ultra purified water from the rinse water source  103 . 
     In one embodiment, the treatment unit  170  may be positioned locally near the polishing station  101 . In another embodiment, the treatment unit  170  may located remotely. In one embodiment, a factory water treatment may be used as the treatment unit  170 . The water stream from the first filtration unit  150  and or from the second filtration unit  160  may be flown to factory water treatment unit for recycling, which may be located outside the building where the factory wide water treatment systems are positioned. 
     Since both polishing and rinsing comprise multiple phases. For example, polishing may be performed in three or more steps to achieve high throughput and high quality. The initial polishing step, such as bulk polishing, is usually more tolerant to variation of polishing slurry than the final polishing step, such as buffing. Therefore, it can be desirable to direct recycled polishing slurry to the polishing station when it performs bulk polishing and shut off the recycled polishing slurry when the polishing station is performing final step buffing. Similarly, initial rinse after polishing is less sensitive to traces of chemical and ions in the rinse water than the final rinse. Therefore, it is desirable to supply recycled rinse water to the polishing station while the polishing station is performing initial rinsing and shut off the recycled rinse water when the polishing station is performing final rinsing. 
     In one embodiment, the polishing system  100  further comprises a system controller  109 . In one embodiment, the system controller  109  may control the multiple valves in the polishing system  100  to insure that recycled polishing slurry and/or rinse water is delivered or shut off at desired time. For simplicity of drawing, connections between the system controllers  109  and the components of the polishing system  100  are not shown. In one embodiment, the system controller  109  is a stand alone independent controller for supplying and recycling polishing slurry. In another embodiment, the system controller  109  is integrated in to a CMP tool controller as an integral part. 
       FIG. 2A  is a schematic chart of a polishing system  200 A having a recycling unit  204  in accordance with another embodiment of the present invention. The polishing system  200 A is similar to the polishing system  100  of  FIG. 1  but with detailed exemplary embodiments for different units. 
     The polishing system  200 A may be configured to planarize substrates comprising variety of materials, such as polycrystalline silicon, single crystalline silicon, oxides, tungsten, copper, aluminum, or combinations of different materials. In one embodiment, the polishing system  200 A may be used to prepare a polycrystalline silicon substrate for solar panel fabrication. 
     The polishing system  200 A comprises a polishing station  201  wherein a substrate  213  being processed is retained by a polishing head  212  and pressed against a polishing pad  211 . The polishing head  212  and the polishing pad  211  both rotate and provide relative motion between the substrate  213  and a polishing surface of the polishing pad  211 . A slurry nozzle  214  provides a polishing slurry to the polishing pad  211 . A rinse nozzle  215  provides rinse water to the polishing station  201 . 
     The polishing system  200 A further comprises a polishing slurry unit  202  configured to supply polishing slurry to the polishing station  201 . The polishing slurry unit  202  comprises a source  221  and a local tank  224 . In one embodiment, the source  221  may be a source tank storing pre-generated the polishing slurry. The source tank is generally much larger than the local tank  224 . In another embodiment, the source  221  may be a slurry generator to generate polishing slurry on-site. During operation, a pump  222  pumps polishing slurry through a filter  223  to the local tank  224 , and a pump  225  from connected to the local tank  224  pumps the slurry through a filter  226  to the slurry nozzle  214 . 
     In one embodiment, the filter  226  may be a point-of-use depth filter and particle filtration to remove any gels and agglomerates just prior to dispensing the polishing slurry to the polishing station  201 . In one embodiment, the filter  226  is disposed downstream to the pump  225  and upstream to a delivery arm to which the slurry nozzle  214  is connected. 
     The polishing system  200 A further comprises a rinse water unit  203  configured to supply rinse water to the polishing station  201  for rinsing of the substrates and/or the polishing station  201 . The rinse water unit  203  may comprise a tank  231  configured for store rinse water for supplying to the rinse nozzle. The tank  231  usually connects to a source of virgin ultra purified water. 
     In one embodiment, the polishing station  201  comprises a collecting bin  216  configured to receive used polishing slurry, rinse fluid along with removed material. In one embodiment, the collecting bin  216  may be lowered during substrate loading and unloading and raised during polishing and rinsing to catch polishing slurry and rinsing fluid. 
     The polishing system  200 A may have a tank  219  connected downstream to the collecting bin  216 . In one embodiment, the tank  219  may be coupled to multiple polishing stations and configured to collect mixtures of used polishing slurry and rinsing fluid from multiple polishing stations. 
     The polishing system  200 A further comprises a recycling unit  204  configured to receive the mixture from the tank  219  and to generate reusable polishing slurry and reusable rinse water from the mixture in the tank  219 . 
     The recycling unit  204  comprises a first filtration unit  250  configured to split received mixture into a water stream with majority of chemicals and particles removed and a concentration stream comprising chemicals and particles. The concentration stream is directed to a second filtration unit  260  to obtain reusable polishing slurry. In one embodiment, the water stream is directed to an optional sanitization unit  280  and a treatment unit  270  to obtain reusable purified water. In another embodiment, the water stream may be directly going to waste. 
     The first filtration unit  250  comprises a pump  251  connected upstream to a filter unit  252 . The pump  251  is configured to pressurize income stream from the tank  219  through the filter unit  252 . The first filtration unit  250  is configured to remove particles that are too large for polishing slurry from the concentration stream. 
     The filter unit  252  comprises suitable filter media, such as depth filter and particle filtration unit. In one embodiment, the filter unit  252  comprises one or more membranes or other filtration technologies. As shown in  FIG. 2A , the filter unit  252  can comprise one or more membranes, such as a microfiltration membrane, a nanofiltration membrane or an ultrafiltration membrane. In one embodiment, the membranes may be disposed in a staged manner. The income stream would go through the one or more membranes in sequence. In one embodiment, the filter unit  252  comprises a microfiltration membrane, a nanofiltration membrane, and an ultrafiltration membrane in sequence. 
     In one embodiment, the first filtration unit  250  comprises a concentration outlet  257  in fluid communication with stream between the microfiltration membrane  253  and the nanofiltration membrane  254 . As a result, large particles from the income stream do not permeate the filter unit  252  and small particles permeate the filter unit  252 . 
     The first filtration unit  250  further comprises a water output  258  in fluid communication with the permeate stream out of the all stages of membranes in the filter unit  252  to output a water stream with most chemical and particles removed. In another embodiment, the stream from the water output  258  may also exit the system as waste. 
     The pump  251  may be a diaphragm pump, a bellow pump, or a magnetically coupled or centrifugal pump. Alternately a vacuum system or gas pressure can be employed for transfer of fluids. In one embodiment, the pump  251  may be a magnetically levitated pump. This low sheer pump has minimum impact on particle size distribution of the polishing slurry. 
     The filter unit  252  may be configured for dead-end filtration, cross flow filtration, or back flushable filtration. In one embodiment, the microfiltration membrane  253 , the nanofiltration membrane  254  and the ultrafiltration membrane  255  may be polymeric membranes or ceramic membranes. The one or more membranes in the filter unit  252  may be spiral membranes, tubular membranes, plate and frame, or hollow fiber membranes. 
     The second filtration unit  260  is connected downstream to the first filtration unit  250  to receive the concentration stream. The second filtration unit  260  is configured to stabilize particle size distribution in the output stream. 
     In one embodiment, the second filtration unit  260  comprises a filter media  262  and a pump  261  configured to pressure the concentration stream through the filter media  262 . In one embodiment, the filter media  262  comprises a membrane. The pump may be a magnetically levitated pump that imposes minimal destruction to the abrasive particles in the polishing slurry. 
     The second filtration unit  260  has a slurry output  264  configured to output a permeated stream, and a back flush port  266  configured to receive a rinse fluid to clean the filter media  262  by backwashing to remove waste. The waste may be exit the second filtration unit  260  through a waste output  265 . In one embodiment, the waste may be about 10% to about 15% of feed stream. In another embodiment, the waste output  265  may be connected to the water recycling branch, such as an inlet of the sanitizing unit  280  for water recycling. 
     In one embodiment, the second filtration unit  260  further comprises a dosing unit  267  configured for keeping the abrasive slurries stabilized during processing in the second filtration unit  260 . The dosing unit  267  may provide an additional stream of conditioning chemicals, such as KOH or NH 4 OH  267  to the second filtration unit  260  either before, during or after filtration. 
     The pump  261  may be a diaphragm pump, a bellow pump, or a magnetically coupled or centrifugal pump. In one embodiment, the pump  261  may be a magnetically levitated pump with minimized impact on particles of the polishing slurry. 
     The filter media  262  may be a polymeric membranes or a ceramic membrane. The filter media  262  may be a spiral membrane, a tubular membrane, or a hollow fiber membrane. 
     The second filtration unit  260  may be a dead-end filtration or a cross-flow filtration. 
     In one embodiment, the slurry out of the second filtration unit  260  may be further filtered with a polishing filtration unit  290  before directed back to a local polishing slurry tank of the polishing station  201  or to the polishing slurry unit  202 . 
     The permeate stream from the slurry output  264  maybe directed to the source  221  or the local tank  224 . 
     The sanitization unit  280  is configured to reduce and control bacteria and or organic contamination from the fluid flowing therethrough, such as the water stream from the first filtration unit  250  and/or the second filtration unit  260 . In one embodiment, the sanitization unit  280  may be an ultra violet (UV) unit configured to oxidize the organic species or kill the bacteria in the water stream. 
     In one embodiment, the sanitized water stream is directly flown back to the polishing station  201  for rinsing or other function. The sanitized water stream may be used in a first rinse, which has low requirement for the purity of the rinse water. 
     The treatment unit  270  is configured to purify and deionize the water stream. In one embodiment, the treatment unit  270  comprises a pump  271 , a reverse osmosis membrane  273  and an ion-exchange resin  274 , which may be regenerated continuously via ion selective membranes. The pump  271  is configured to pressurize incoming flow to the reverse osmosis membrane  273  and the ion-exchange resin  274 . The output stream from an outlet  276  of the treatment unit  270  results in ultra purified water. The rejected stream from the treatment unit  270  exits through a waste output  278  as waste water. In one embodiment, the waste water is between about 5% to about 20% of feed stream. The purified water from the treatment unit  270  may be sent back to directly to the polishing station  201  or to mix with virgin ultra purified water from a rinse water inlet  232 . 
     In one embodiment, the treatment unit  270  is a stand alone water recycling unit. In another embodiment, the treatment unit  270  belongs to a pre-existing factory water treatment system. 
     In one embodiment, the polishing system  200 A further comprises a system controller  209 . In one embodiment, the system controller  209  may control the multiple valves in the polishing system  200 A to insure that recycled polishing slurry and/or rinse water is delivered or shut off at desired time. For simplicity of drawing, connections between the system controllers  209  and the components of the polishing system  200 A are not shown. 
     The membranes used in each filtration/treatment unit  250 ,  260 ,  270  may be one of depth filter, a spiral membrane, a hollow fiber membrane, a tubular membrane, a plate and frame membrane operated in a dead-end filtration method, a back flushable filtration method, or in a cross flow filtration method. 
     In one embodiment, the system controller  209  is a stand alone independent controller for supplying and recycling polishing slurry. In another embodiment, the system controller  209  is integrated in to a CMP tool controller or implemented as a slave to the CMP tool control system. 
     In one embodiment, the system controller  209  is connected to at least one of the reservoir pumps  222 ,  225  and the filtration pumps  251 ,  261 ,  271 . The system controller  209  is configured to monitor and/or adjust characteristics of polishing slurry according to process parameters of the at least one pump connected to the system controller  209 . In one embodiment, the at least pump connected to the system controller  209  is a centrifugal pump, such as an electromagnetically levitated centrifugal pump. 
     Each of the pumps  222 ,  225 ,  251 ,  261 ,  271  may be one of a piston pump, a diaphragm pump, a bellow pump, a peristaltic pump, a magnetically levitated centrifugal pump, and a device for fluid transfer by vacuum draw. In one embodiment, each of the pumps  222 ,  225 ,  251 ,  261 ,  271  may be a centrifugal pump. Centrifugal pumps provide more controlled shear forces than pumps traditionally used for polishing slurry and/or polishing slurry waste transportation. The high sear forces reduce particle agglomeration drastically. In one embodiment, each of the pumps  222 ,  225 ,  251 ,  261 ,  271  is a magnetically levitated centrifugal pump. Magnetically levitated pumps add very few particles to the fluid, therefore, reducing particle contamination and damages to substrate being processed. An exemplary magnetically levitated centrifugal pump may made by Levitronix, Switzerland. 
     In one embodiment, connecting the system controller  209  to at least one magnetically levitated centrifugal pump enables return of real time rheology measurements and/or torque requirements on each slurry blending and recycling step. Rheology measurements and/torque requirement can be obtained from pumps at one or more of the following positions: a position where recycled slurry is blended into virgin slurry, a position wherein slurry recycles back to a main reservoir, a position driving agglomeration filtration, a position transport past large reservoir, a position transport past local reservoir, a position feeding polishing slurry to the polishing pad. 
     In one embodiment, magnetically levitated centrifugal pumps may be used to meter polishing slurry to local reservoir or to polishing pads. 
     In one embodiment, magnetically levitated centrifugal pumps may be used to afford appropriate levels of shear to the polishing slurry to positively impact rheology and minimize agglomeration. 
     In another embodiment, magnetically levitated centrifugal pumps may be used to inject and mix additives, to mix/combine various streams of virgin slurry, recycled polishing slurry, water, and/or chemical additive packages. 
     In another embodiment, other metrology sensors positioned adjacent pump housing may be used in addition to or incorporation of magnetically levitated centrifugal pumps. 
     In another embodiment, magnetically levitated centrifugal pumps may be used to monitor the back pressure of feed to the filtration and back wash media to (1) alert to plugging issues that would require filtration maintenance, (2) adjust pumping power to compensate for increased pressure drop until process is finished and shut down without interrupting process, and (3) initiate additional frequency, increased flow during cross flow or back wash steps, or optionally inject a cleaning agent bypass the current polishing slurry and ultra purified water recycle until the clean agent is purged as predetermined by the control software based on set point parameters. 
     In another embodiment, magnetically levitated centrifugal pumps may be used to provide feedback to the optional integrated controls system that manages the CMP water and slurry recycle system as a holistic set of unit operations along with the CMP tool and water plant rather than operating as a cluster of individually controlled circuits. 
     In another embodiment, magnetically levitated centrifugal pumps may be used to lower levels of contamination due to complete encapsulation of all moving parts with an inert polymer and the absence of metal or ceramic drive seals in the pumping system. 
       FIG. 2B  is a schematic view of a polishing system  200 B with one embodiment of the present invention. The polishing system  200 B is similar to the polishing system  200 A of  FIG. 2A , except that the polishing system  200 B has a separation unit  295  configured to separate polymeric particles or large particles, such as large silicon oxide particle, from the flow before recycling. In one embodiment, the separation unit  295  is a centrifugal separator. The separated particles may exit the system from an outlet  296 . 
       FIG. 2C  is a schematic view of a polishing system  200 C in accordance with one embodiment of the present invention. The polishing system  200 C is similar to the polishing system  200 B of  FIG. 2B  except that the separator unit  295  is disposed down stream of the first filtration unit  250 . 
       FIG. 2D  is a schematic view of a polishing system  200 D in accordance with one embodiment of the present invention. The polishing system  200 D is similar to the polishing system  200 A of  FIG. 2D , except that the polishing system  200 D use a diverter valve  294  to separate a water stream and a concentrations stream in stead of using the first filtration unit  250  as in the polishing system  200 A. 
     The diverter valve  294  is connected to the collecting bin  216  of the polishing station  201 . The collecting pin  216  may be stationary or movable. In one embodiment, the diverter valve  294  is configured to direct the content in the collecting bin  216  to the second filtration unit  260  for slurry recycling or to the treatment unit  270  for water recycling. In one embodiment, the diverter valve  294  is a three way valve. The status of the diverter valve  294  may be controlled by the system controller according to the process in the polishing station  201 . For example, the diverter valve  294  may be adjusted to direct the flow to the second filtration unit  260  for slurry recycling when there is polishing slurry flowing from the slurry nozzle  214  to the polishing station  201 , and adjusted to direct the flow towards the treatment unit  270  during rinsing or there no slurry flow from upstream. 
     In one embodiment, the polishing system  200 D comprises an optional separation unit  295  connected between the diverter valve  294  and the second filtration unit  260  to remove polymeric particles and/or large particle prior to the slurry recycling. 
       FIG. 3  is a schematic chart of a polishing system  300  having a dedicated recycled slurry tank  324  and a dedicated virgin slurry tank  327  in accordance with another embodiment of the present invention. The polishing system  300  is similar to the polishing system  200  of  FIG. 2 , except for the difference in the slurry unit  302 . 
     The slurry unit  302  is configured to provide the polishing station  301  with virgin polishing slurry without mixing with the recycled slurry during polishing. This allows the polishing station  301  to perform multiple steps of polishing and use recycled polishing slurry only when process parameter permits. 
       FIG. 4  is a schematic chart of a polishing system  400  having a dedicated recycled rinse water tank  432  in accordance with another embodiment of the present invention. The polishing system  400  is similar to the polishing system  200  of  FIG. 2 , except for the difference in the rinse water unit  403 . 
     The rinse water unit  403  comprises a recycled rinse water tank  432  to receive recycled rinse water and a virgin rinse water tank  431  without recycled rinse water. This allows the polishing station  301  to perform multiple rinsing and use recycled rinse water only when process parameter permits, such as during initial rinsing. 
       FIG. 5  is a schematic chart of a polishing system  500  having multiple polishing stations  501   a ,  501   b ,  501   c  and a recycling unit  504  in accordance with another embodiment of the present invention. The polishing system  500  is configured to perform multiple polishing steps. Each polishing station  501   a ,  501   b ,  501   c  is dedicated to a polishing step with different polishing rate. 
     The polishing waste from the polishing stations  501   a ,  501   b ,  501   c  is gathered in a tank  519  and sent to the recycling unit  504 , which is similar to the recycling units  104  and  204  described above. 
     A polishing source  502  provides recycled and virgin polishing slurry to the polishing stations  501   a ,  501   b ,  501   c . In one embodiment, the recycled polishing slurry is only supplied to the polishing station that is configured to perform bulk polishing. 
     A rinse water source  503  is configured to selectively supply recycled rinse water and virgin rinse slurry to each polishing station. 
     Even though three polishing stations are shown in  FIG. 5 , more or less polishing stations may be used according to process requirement. 
     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.