Abstract:
Wastewater from a chemical-mechanical polishing process (CMP) used in semiconductor chip fabrication has hitherto been, and is still being, discharged into the public sewage system after chemical neutralization and sedimentation. This has the drawback that water consumption is considerable. It is therefore an object of the invention to reduce the total amount of wastewater produced that has to be discharged. This is achieved by the wastewater to be treated being subjected to an ultra-filtration. This allows the treated CMP wastewater to be reused within the plant. In particular, it can be recycled in order again to recover therefrom deionized water of a very high purity for operational purposes, e.g. for CMP.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a division of U.S. application Ser. No. 09/428,582, filed Oct. 28, 1999, which was a continuation of copending International Application PCT/DE98/01164, filed Apr. 27, 1998, which designated the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The invention relates to an apparatus for treating wastewater from a chemical-mechanical polishing process used in chip fabrication. 
     Chemical-mechanical polishing processes (CMP) are used in semiconductor chip fabrication to planarize the semiconductor wafer or to keep it planar. This involves treating the wafer with a polishing tool with the addition of a polishing fluid, the so-called slurry. Typically, deionized water with a very high purity serves as a basis for the polishing fluid, which is added to chemical additives and/or particles having an abrasive effect. 
     After the chemical-mechanical polishing process, the polishing fluid running off will, as well as its constituents, additionally contain abraded material from the polishing process and further contaminants. As a result, the polishing fluid is laden with a series of particles having an abrasive effect and a series of chemically active substances. In the case of a wastewater load of about 30 m 3 /h, the following constituents may be present, for example, in the polishing fluid. 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 TMAH (3% strength) 
                 = 
                 ˜80 
                 l/h 
               
               
                   
                 SiO 2   
                 = 
                 ˜17.2 
                 kg/h 
               
               
                   
                 Al 2 (SO 4 ) 3  (8% strength) 
                 = 
                 ˜9 
                 l/h 
               
               
                   
                 NH 4 OH (2% strength) 
                 = 
                 ˜14 
                 l/h 
               
               
                   
                 Fe(NO 3 ) (49% strength) 
                 = 
                 ˜7 
                 l/h 
               
               
                   
                 Al 2 O 3   
                 = 
                 ˜0.6 
                 kg/h 
               
               
                   
                 As 
                 = 
                 ˜35 
                 mg/h 
               
               
                   
                 HNO 3   
                 = 
                 ˜250 
                 g/h 
               
               
                   
                 TiN x   
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 H 3 PO 4   
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 KOH 
                 = 
                 ˜250 
                 g/h 
               
               
                   
                 HF 
                 = 
                 ˜0.1 
                 g/h 
               
               
                   
                 H 2 O 2   
                 = 
                 ˜0.1 
                 g/h 
               
               
                   
                 W 
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 Al 
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 (NH 4 ) 2 S 2 O 8   
                 = 
                 ˜150 
                 g/h 
               
               
                   
                 HCl 
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 NH 4 F 
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 Monoethylene glycol 
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 Ammonium perfluoralcylsulfonate 
                 = 
                 ˜100 
                 g/h 
               
               
                   
                 (NH 4 )Ce(NO 3 ) 6   
                 = 
                 ˜100 
                 g/h 
               
               
                   
                   
               
             
          
         
       
     
     Up till now, the wastewater from a chemical-mechanical polishing process used in chip fabrication has been neutralized chemically, coarse particle contamination is removed by sedimentation, and the wastewater thus treated is passed to the public sewage system and is thus lost for operational purposes. 
     The known procedure has the drawback that water consumption is considerable; in relatively large chip fabrication plants it is a few m 3 /h. This amount of water discharged into the public sewage system must be replaced by fresh deionized water of a very high purity, thus entailing corresponding costs of providing the deionized water. Moreover, the wastewater coming from a chemical-mechanical polishing process in chip fabrication causes an additional load to the water treatment plants of the public sewage system, which is environmentally undesirable. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an apparatus for treating wastewater from a chemical-mechanical polishing process used in chip fabrication that overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which permit a reduction in the total amount of wastewater produced and to be discharged. In particular, it is desirable, as a development of the invention, for the treated wastewater to be capable of being recycled subsequently to produce deionized water. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for treating wastewater from a chemical-mechanical polishing process used in chip fabrication, the wastewater containing particles having an abrasive effect and chemically active substances attacking the particles having the abrasive effect, which includes removing rapidly the particles having the abrasive effect from the wastewater via ultra-filtration in an ultra-filtration facility such the particles are not substantially dissolved by the chemically active substances present in the wastewater and resulting in ultrafiltrated wastewater. 
     The use of the ultra-filtration facility allows the wastewater from a chemical-mechanical polishing process (hereinafter simply referred to as CMP wastewater) to be regenerated in such a way as to allow the treated wastewater to be reused within the plant or to be passed to the public sewage system without significant pollution. Ultra-filtration for the purpose of the patent application results in that particles having a diameter of more than 0.4 μm are essentially filtered out. Moreover, it is preferred for particles having a diameter of more than 0.1 μm to be essentially filtered out by the ultra-filtration. In the case of relatively low to medium particle contamination, ultra-filtration is adequate to achieve such a degree of purity of the treated wastewater as to allow the treated wastewater to be subsequently recycled to produce deionized water. 
     In the process, the CMP wastewater is preferably subjected so rapidly to ultra-filtration, that the particles having an abrasive effect, for example the SiO 2  particles, which are present in the CMP wastewater are essentially not dissolved by the chemically active substances, for example KOH, present in the CMP wastewater. If this is ensured, the substances present in the particles can be almost completely removed from the CMP wastewater by the ultra-filtration. 
     It is further preferred for the particles filtered out in the ultra-filtration facility to be removed from the ultra-filtration facility by back flushing. In the process, it is moreover preferred for the back flushing to occur at sufficiently short intervals for essentially no reaction in the ultra-filtration facility to take place between the particles retained in the ultra-filtration facility and the chemically active substances present in the CMP wastewater. 
     In the case of organic or inorganic contaminants it may be necessary also to provide a reverse-osmosis stage and/or a nano-filtration stage in addition to the ultra-filtration stage. Reverse osmosis here essentially serves to remove organic-chemistry carbon compounds from the CMP wastewater to be treated. Nano-filtration for the purpose of this patent application results in that particles having a diameter of more than 0.05 μm are essentially filtered out. Moreover, it is preferred for particles having a diameter of more than 0.01 μm to be essentially filtered out by the nano-filtration. 
     It is particularly economical for the ultra-filtration of the wastewater to be treated to be followed by the measurement of one or more parameter values of the ultrafiltrated wastewater. The ultrafiltrated wastewater, depending on the parameter values measured, to be either passed on directly or passed to a reverse-osmosis facility or a nano-filtration facility or both. Thus, the further, more expensive cleaning stages of reverse osmosis and nano-filtration are used only if they are actually required according to the parameter values measured. Relevant parameter values include, in particular, the conductivity of the treated wastewater, its total content of organic carbon, its particle content or its level of silicon oxides or ammonia NH 3 . 
     Preferably, the purified wastewater is subsequently again fed to a regeneration facility for producing deionized water, thus resulting in a closed water cycle. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in an apparatus for treating wastewater from a chemical-mechanical polishing process used in chip fabrication, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a  and  1   b  are diagrammatic, block diagrams showing a first exemplary embodiment of an apparatus containing an ultra-filtration facility according to the invention; and 
     FIGS. 2 a ,  2   b , and  2   c  are block diagrams showing a second exemplary embodiment of the apparatus additionally containing a reverse-osmosis facility and/or a nano-filtration facility. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIGS. 1 a  and  1   b  thereof, there is shown a block diagram of a wastewater treatment apparatus which, in particular, is for CMP wastewater containing solely particle contamination. At the right side, FIG. 1 b  connects to FIG. 1 a , the corresponding junctions of the conduits designated by “a”, “b”, “c” respectively. 
     Via an input conduit  1 , the CMP wastewater is fed to a lifting facility  2 . Via conduits  4 ,  6  the CMP wastewater then passes into a feed tank  7 . Both the lifting facility  2  and the feed tank  7  are equipped with fill level measurement equipment  8  and limit switches  9 . 
     A pump  10  delivers the CMP wastewater from the feed tank  7  via a conduit  11  to an ultra-filtration facility  12 . In the ultra-filtration facility  12  of FIGS. 1 a  and  1   b , essentially all particles having a diameter of more than 0.2 μm are filtered out. 
     In this configuration, the conduits  1 ,  4  and  6 , the lifting facility  2 , the feed tank  7  and the pump  10  are of such a configuration that the particles, for example SiO 2  particles, which are present in the CMP wastewater and have an abrasive effect are essentially not dissolved by the chemically active substances, for example KOH, present in the CMP wastewater. 
     Under standard process conditions, up to over 99% of the CMP wastewater stream entering the ultra-filtration facility  12  leaves the ultra-filtration facility  12  as a filtered permeate via a conduit  14 , although the percentages achievable in practice do depend, in specific situations, on wastewater load and type and degree of pollution. The conductivity of the permeate in the conduit  14  is measured by a control system sensor  15  and a measuring sensor  16 . In the exemplary embodiment of FIGS. 1 a ,  1   b  the requirement is for the conductivity value of the purified wastewater in the conduit  14  to be less than 500 μS/cm. If this limit is complied with, the purified wastewater will pass, via the conduit  14 , a valve  18  and an adjoining output conduit  17 , to a water regeneration facility  100  of a known configuration and is there recycled to produce deionized water which, for example, can be reused in the CMP process. 
     At regular intervals, the particles filtered out are removed from the ultra-filtration facility  12  by back-flushing. To this end, the inflow of the CMP water from the conduit  11  is briefly stopped, and already filtered wastewater from the conduit  14  flows in the reverse direction to the ultra-filtration facility  12 . The concentrate filtered off is then passed, via a conduit  13 , to a neutralization and sedimentation facility operating in a standard manner (not shown in FIGS. 1 a ,  1   b ). The intervals between individual back-flushing operations chosen in this context are sufficiently short for essentially no reaction to take place in the ultra-filtration facility  12 , during normal operation, between the particles retained in the ultra-filtration facility  12  and the chemically active substances present in the CMP wastewater. 
     As previously mentioned, as a rule there is a requirement for the conductivity value of the purified wastewater in the conduit  14  to be less than 500 μS/cm. If the conductivity limit of 500 μS/cm is exceeded by less than 50%, a converter actuator  19  controlled by a control system sensor  15  opens, via a control line  20 , a valve  21  and passes the ultra-filtrated wastewater from the conduit  14  via a conduit  22  back to the feed tank  7 . At the same time, the valve  18  between the conduit  14  and the output conduit  17  is closed via a control line  23 . 
     In the event of the conductivity limit is exceeded by more than 100%, the converter actuator  19  controlled by the control system sensor  15  opens, via a control line  24 , a valve  25  so that the wastewater from the ultra-filtration facility  12  in the conduit  14  is passed to a storage tank  27  via a conduit  26 . Such a severe breach of the limit will largely occur in the event of a rupture of the filter membrane in the ultra-filtration facility  12 . The valve  18  between the conduit  14  and the output conduit  17  remains closed. 
     The wastewater in the storage tank  27  can be passed on, via a set of pumps  28  and an output conduit  29 , to be neutralized and sedimented in a known manner. The storage tank  27  is likewise equipped with the fill level measuring device  8  and the limit switch  9 . 
     The invention further envisages that the fill level measuring device  8  of the feed tank  7 , upon too high a fill level in the feed tank  7  being reached, shall, via a control line  30 , close a valve  31  in the conduit  6  and at the same time open a valve  32  in a conduit  5  which runs to the storage tank  27  and connects to the conduit  4 , so that CMP wastewater to be purified, which flows in from the lifting facility  2  via the set of pumps  3  and the conduit  4  will reach the storage tank  27  and then be pumped off via the set of pumps  28  and the output conduit  29 . 
     It is also provided that part of the wastewater purified in the ultra-filtration facility  12  can be drawn off from the conduit  14  via a pump  33  and an output conduit  34  and can be passed to the CMP wastewater treatment facility shown in FIGS. 2 a ,  2   b ,  2   c  for the purpose of other parameter values being measured and/or for further cleaning. 
     The CMP wastewater treatment facility of FIGS. 1 a ,  1   b  is configured for a CMP wastewater production of about 20 m 3 /h. The purity limits of the purified wastewater in the output conduit  17  that are reached in practice are: conductivity (s) &lt;500 μS/cm, total organic carbon content (TOC) &lt;3 mg/l, fewer than 100 particles having a diameter of &lt;0.4 μm per l. Given an inflow of 20 m 3 /h of CMP wastewater in the input conduit  1 , less than 200 l/h of wastewater concentrate will be passed on under normal operating conditions via the output conduit  13  for neutralization and sedimentation, while more than 19.8 m 3 /h—more than 99%—can be passed on, via the output conduit  17 , for recycling to be produced as deionized water. This data clearly illustrate the considerable reduction in the amount of water consumed in chemical-mechanical polishing which is achieved by the invention. 
     The exemplary embodiment of FIGS. 2 a ,  2   b ,  2   c  has been expanded by a reverse-osmosis and/or nano-filtration facility  40 , compared with the first exemplary embodiment of FIGS. 1 a ,  1   b . FIGS. 2 a ,  2   b ,  2   c  in combinations schematically show a block diagram of the wastewater treatment apparatus. FIG. 2 b  connects to FIG. 2 a  on the right, and FIG. 2 c  connects to FIG. 2 b  on the right, the corresponding junctions of the conduits being designated, respectively, by “a”, “b”, “c”, “d”, “e”, “f”. 
     While the wastewater treatment facility of FIGS. 1 a ,  1   b  is configured for CMP wastewaters with low to medium contamination by particles, the wastewater treatment facility of FIGS. 2 a ,  2   b ,  2   c  is additionally suitable for treating CMP wastewaters containing chemical contaminants. In particular, this may involve contamination by arsenic and/or tetramethylammonium hydroxide. 
     Since the configuration of the apparatus of FIGS. 2 a ,  2   b ,  2   c  is highly similar to the apparatus of FIGS. 1 a ,  1   b , only the differences will be discussed hereinafter; apart from those, the reader is referred to the explanation relating to FIGS. 1 a ,  1   b.    
     Via the input conduit  1 , CMP wastewater containing arsenic and/or tetramethylammonium hydroxide flows into the wastewater treatment facility of FIGS. 2 a ,  2   b ,  2   c . The entire facility of FIGS. 2 a ,  2   b ,  2   c  is configured for a wastewater throughput of about 10 m 3 /h. The prepurified wastewater leaving the ultra-filtration facility  12  is passed to the reverse-osmosis and/or nano-filtration facility  40  via a conduit  41  into which a pump  42  is incorporated. The wastewater purified in two stages leaves the reverse-osmosis and/or nano-filtration facility  40  via the conduit  14 . The filtered-off concentrate from the ultra-filtration facility  12 , the concentrate being produced, under normal operating conditions, at a rate of about 100 l/h, passes via the output conduit  13   a  into a treatment facility not shown in FIGS. 2 a ,  2   b ,  2   c . A further neutralization and sedimentation of the filtered-off concentrate takes place in the treatment facility known per se. In the event of non-negligible arsenic fractions still being found in the filtered-off concentrate, an arsenic precipitation may additionally be carried out in a manner known per se. 
     This treatment facility is also reached, via an output conduit  43 , by the filtered-off concentrate and/or the solution, concentrated by reverse-osmosis, from the reverse-osmosis and/or nano-filtration facility  40 , which concentrate or solution is produced at a rate of about 1000 l/h under normal operating conditions. In the course of the nano-filtration in the nano-filtration facility  40  of FIGS. 2 a ,  2   b ,  2   c , essentially all the particles having a diameter of more than 0.05 μm are filtered out. 
     The same treatment facility may also be reached, via the set of pumps  28  and an output conduit  29   a , by CMP wastewater from the storage tank  27 . 
     The invention further envisages that the conduit  14  is connected to a sampling pump  44 . The sampling pump  44  draws small amounts of wastewater purified in two stages from the conduit  14  and returns the test water via valves  45 , intermediate storage tank  46  and conduits  47 ,  48  back to the feed tank  7 . Connected to the intermediate storage tanks  46  are sensors  49  that carry out on-line measurements of the total organic carbon content (TOC) and of the number of particles. These measured values, together with the conductivity value of the wastewater in the conduit  14 , measured by the measuring sensor  16  and the control system sensor  15 , are relayed via signal lines  50  to the converter actuator  19  for evaluation. 
     Also debouching into the conduit  47  is the conduit  34  from the pump  33  of the wastewater treatment facility of FIGS. 1 a ,  1   b , so that the ultra-filtrated wastewater in the output conduit  17  in the facility of FIGS. 1 a ,  1   b  can be tested, if required, by the sensors  49  for its total organic carbon content and particle content. 
     The wastewater treatment facility of FIGS. 2 a ,  2   b ,  2   c  allows—beyond the limits achievable by the facility of FIGS. 1 a ,  1   b —a total organic carbon content (TOC) of less than 2 mg/l to be achieved in the CMP wastewater, purified in two stages, in the output conduit  17  of FIGS. 2 a ,  2   b ,  2   c . Of the CMP wastewaters flowing in at about 10 m 3 /h, about 8.9 m 3 /h are returned again in the facility of FIGS. 2 a ,  2   b ,  2   c , via the output conduit  17 , to the regeneration facility for deionized water and are recycled, only about 1.1 m 3 /h being removed for the cycle and being passed on to the treatment facility for neutralization and sedimentation.