Patent Publication Number: US-8528593-B2

Title: Bleed and feed device and method

Description:
Bleed and feed devices and methods are employed in many chemical production processes, such as, for example, in semiconductor manufacturing. 
     The aim of this type of subsequent dispensing is to achieve constant concentrations of the individual substances in a mixture or bath during production over a longer period. With this mode of operation, it is also possible to keep substances, which accumulate during the length of use, constant during the dilution. 
     This is usually achieved with a ‘feed’ solution, which has a higher concentration than the nominal concentration and only contains the substances which are used. The addition of the feed solution is mostly carried out in load dependent time intervals with constant volumes. For example, between 5% and 30% of the whole bath volume is replaced once a day. 
     The ‘bleed’, that is to say, the removal, is carried out by a passive overflow at the tank or by a pump, which is controlled by a maximum-minimum sensor. Decomposition products, which develop during the production process, are regularly diluted in this way, and can be kept under a critical concentration over a longer period. 
     This concept of process control has several disadvantages, especially in processes which place higher requirements on the constancy of the concentration of the individual substances in the mixture, such as, for example, semi conductor technology. As a result of the supply in time intervals, the system determines a sawtooth course of the concentrations in the mixture. The production process must also be partly stopped at the time of supply, since the volume and the concentrations in the tank fluctuate depending on the products which are in the tank or the process chamber. Furthermore, the delivered feed solutions are subject to concentration fluctuations due to the production process. All of these fluctuations lead to varying results for products produced in demanding processes, and in the worst case, to rejection or failures in use of the products to be made. In addition, it is hard to fulfil in practice the requirement that only substances used are to be present in the feed solution. 
     In the US patent application 2004/0142566 A1, it is suggested that a smaller amount of the bath is replaced in shorter time intervals, so that the total desired refill is achieved gradually over a time period of 24 hours. In this method, the typical interval time of 24 hours is reduced to 30-60 minutes. In the method known in this U.S. patent application, bleed solution is taken from the storage tank, and dispensed into a second container, and the amount of bleed solution in the second container is measured and then disposed of. Subsequently, the second container is filled with a predetermined amount of a new solution (feed solution) from the storage tank, and the predetermined amount of feed solution is dispensed into the storage tank, in order to ensure that the fed and discharged volume is the same, and therefore does not change the volume in the tank. 
     Finally, the disadvantage of this method is that is does not work continuously over a longer period. Furthermore, due to the intermediate storage of bleed and feed solutions in the second container, there is the danger of contamination of the feed solution. 
     The object of the present invention is to provide a bleed and feed method, in which contamination is avoided, which works quasi-continuously or continuously, and can be implemented in demanding processes such as the production of semi conductor elements, as well as to give a system in which the method can be carried out. 
     The object is achieved according to the invention by the features of claims  1  and  13 . 
     In the method according to the invention, a first receiving space G 1  for the feed solution is provided between the tank T 1  for the feed solution and the process tank PT, and correspondingly, a second receiving space G 2  for the bleed solution is provided between the process tank PT and the tank T 2  for the bleed solution. The first receiving space G 1  is filled with feed solution from the tank T 1 . Subsequently, the feed solution is pumped from the first receiving space G 1  by means of a pump into the process tank, whereby the volume of the amount of feed solution delivered into the process tank is measured. 
     In a similar way, by measuring the volumes of the bleed solution, the bleed solution is pumped by means of the pump P 3  from the process tank PT into the second receiving space G 2  for the bleed solution, and the bleed solution is subsequently emptied into tank T 2 . 
     The contamination of the feed solution is avoided as a result of the feed solution according to the invention being temporarily stored in a different receiving space from the bleed solution. 
     Furthermore, in order to increase the accuracy of the respective volume flows, according to the invention the volumes into or out of the process tank PT are not only measured, but also calculated on the basis of the pumping power of the pumps P 2  and P 3 , and a correction factor is calculated from the difference of the measured and calculated volumes, which is used to correct the nominal delivery volume of the pumps P 2  and P 3  in the next cycle. 
     In order to guarantee the required accuracy of the process, the containers G 1  and G 2  should be constructed in such a way that the error in determining volumes in these containers should be less than 0.1%, preferably less than 0.05%, and particularly preferably, less than 0.02%. 
     The absolute volume of G 1  and G 2  is determined by the maximal required bleed and feed rate, the volume of the process tank PT and the required process window, whereby the dispensing accuracy depends purely and simply on the reproducibility of the volumes of containers G 1  and G 2  over a much longer time period. 
     The volume flow of the feed solution for filling the first receiving space G 1  is preferably a multiple of the volume flow of the feed solution out of the first receiving space G 1  into the process tank PT, in particular at least double, preferably at least 5 times the value, and particularly preferably, at least 20 times the value. Due to the high volume flows into the first receiving space G 1 , and the short filling period resulting from this, higher accuracy can be achieved by the control according to the invention. 
     The time, in which the bleed solution is pumped by means of the pump P 3  from the process tank PT into the second receiving space G 2 , should also be a multiple of time in which the bleed solution is emptied out of the second receiving space G 2  into the tank T 2 , preferably at least double. 
     A continually working method can be realised in that filling the first receiving space G 1  (or emptying the receiving space G 2 ) by tank T 1  (or into Tank  2 ), and emptying the first receiving space G 1  (or filling the receiving space G 2 ) into the or out of the process tank PT is done by different pipelines, and the pumps P 2  and P 3  are not switched off during a bleed and feed cycle. In this process, the signals of sensors S 1 , S 2 , S 3  and S 4  in/on the first and second receiving space G 1  and G 2  are used for calculating the correction factors K 1  and K 2  for the pumps P 2  and P 3 . 
     In contrast to this continuously working system, in the previously described easier system, the sensors are exclusively used to refill the container G 1  and to empty the container G 2 . The result of this is that the filling quantity is always constant, and so can be used for calculation of the correction factor. 
     Furthermore, this correction can be improved in that the volume correction V K1  of the first interim container G 1  of the next cycle is calculated from the nominal volume, the correction volume of the last cycle V 1K-1 , the calibrated volume V G1  and the volume delivered by the calibrated filling level. The failed volume of the last cycle is therefore corrected in the next cycle by means of the nominal quantity of the complete last cycle multiplied by the quotient from the new and old correction factor. This amount must then be transmitted in the volume flow offset for a certain period, which should be short, if possible, and should be maximal one cycle. 
     In the frame of the present invention, a characteristic curve correction of the pumps P 2  and P 3  is therefore carried out. The correction of the feed volume flow for external feed flows and the correction of the bleed volume flow for external bleed flows (for example, by evaporation, analysis etc) also takes place. 
     Due to the corrections according to the invention, synchronicity of the bleed and feed flows is not possible. 
     Furthermore, the invention relates to a system for carrying out a bleed and feed method, which comprises a tank T 1  and T 2  for each feed or bleed solution, as well as a first receiving space G 1  for interim storage of the feed solution and a second receiving space G 2  for interim storage of the bleed solution, and a process tank PT as well as pumps P 1 , P 4  for liquid transport between tank T 1 , T 2  and receiving space G 1 , and G 2  and pumps P 2 , P 3  for liquid transport between the receiving space G 1 , G 2  and the process tank PT, sensors S 1 , S 2 , S 3  and S 4  for triggering predetermined filling levels in the receiving spaces G 1 , G 2 , valves (V 1 , V 4 ), as well as a process control computer PR, which controls the flow of the bleed or feed solution out of or into the process tank PT. 
     Of course, the method according to the invention can also be carried out with several feed systems and also with several bleed systems and several feed systems, whereby for each system, corresponding receiving spaces, tanks and pumps are to be provided. 
     The invention also concerns the extension of the bleed and feed system by an analysis system, and by an additional system for processing of the bleed solution. The correction of the volume flow can be done by analysis of the bleed substances, analysis of the feed substances and/or analysis of the reprocessed bleed liquid. 
    
    
     
       The invention will be described in more detail using the following embodiments. 
       In the drawings: 
         FIG. 1  shows the construction in principle of the bleed and feed device according to the invention, 
         FIG. 2  shows the signals of the sensors and regulation of the pumps during a bleed and feed cycle with concentration course and volume course depending on the time for the system according to  FIG. 1 . 
         FIG. 3  the bleed and feed device from  FIG. 1  with a separate supply and removal into or from the receiving spaces G 1  and G 2 , 
         FIG. 4  shows the signals of the sensors and regulation of the pumps during a bleed and feed cycle with concentration course and volume course depending on the time for the system according to  FIG. 3 . 
         FIG. 5  shows the signals of the sensors and regulation of the pumps during a bleed and feed cycle according to adjustment of tolerance-related inaccuracy for the system in  FIG. 3 . 
         FIG. 6  shows a block diagram of regulation and control of the pumps for the device in  FIG. 3 . 
         FIG. 7  shows a bleed and feed system with subsequent dispensing. 
         FIG. 8  shows a bleed and feed system with an additional analysis system. 
         FIG. 9  shows a bleed and feed system with additional analytics and processing. 
     
    
    
     The construction in principle of the bleed and feed system is shown in  FIG. 1 . The feed solution is pumped with a high rate of flow out of tank T 1  with the pump P 1 , opened valve V 1  and closed valve V 2  into the first receiving space G 1  for the feed solution, which is formed as an interim container. The sensor S 2  responds, so the valve V 1  is closed and pump P 1  is stopped (cf. also  FIG. 2 ). This filling process of the interim container typically lasts a few seconds, up to a maximum of a few minutes. 
     Subsequently, the pump P 2  is started and the valve V 2  is opened. The process control computer PR controls the flow rate of the pump P 2 , in order to obtain the desired volume flow of the feed solution into the process tank PT, whereby the interim container is emptied. The sensor S 1  responds, so valve V 2  is closed and pump P 2  switched off (cf.  FIG. 2 ) and the filling process of the interim container G 1  begins again, as described above. 
     A feed cycle can last typically between 30 minutes up to several hours. 
     The same principle as the feed solution is followed for the bleed solution. The bleed solution is pumped by means of the pump P 3  out of the process tank PT with the opened valve V 3  and closed valve V 4  into the second receiving space G 2  for the bleed solution, which in this embodiment is also formed as an interim container G 2 . The sensor S 4  responds, so valve V 3  is closed and pump P 3  switched off. The interim container G 2  is subsequently emptied with a high flow rate into the tank T 2 , in which the pump P 4  is switched on and the valve V 4  is opened. The sensor S 3  responds, so valve V 4  is closed and pump P 4  switched off. 
     Subsequently, pump P 3  is switched on and valve V 3  is opened, and a new bleed cycle begins. A cycle can typically last from 30 minutes up to several hours. 
     The volume between the responses of the sensor S 2  and the decrease of the sensor S 1  in the interim container G 1 , which includes the corresponding mixture of chemicals, must be precisely measured. A corresponding method is used with the second interim container G 2 . 
     Therefore the measured volume V FE  and V BL , which the pumps P 2  and P 3  delivered in a cycle in a certain time period, is known. 
     The construction of the interim containers G 1  and G 2  with the associated sensors S 1 , S 2 , S 3  and S 4  must be formed so that a very high repeat accuracy (long-term stability) of the calibrated volume in G 1  and G 2  is guaranteed. 
     When short-term stable types of pump are used for P 2  and P 3 , the process control computer PR can exactly calculate the delivery volume for each time. In each cycle, a correction factor can be generated for each pump P 2  and P 3 . With these correction factors, the nominal value delivery volumes of the pump are corrected, so that the control can set the pumps very exactly to an exact delivery volume. These correction values are newly calculated for each cycle and adapted for the next cycle if necessary. After completion of a cycle, if a difference between the nominal and actual volumes is found, this will be taken into account in the calculation of the delivery volumes in the next cycle, and possible mistakes are corrected. 
     If a seal develops on the pump P 2  or P 3 , this quickly changes the correction factor, or the correction factor differs greatly from its nominal value. This can be determined by the process control computer PR, and the user is given a tip on a necessary repair, before it comes to a failure. 
     The pump time of the pumps P 1  and P 4  is to be monitored in the same way. A tip can be given to the user on a large change of value, although the accuracy requirements on P 1  and P 4  are not so large. It is only important that the maximum filling or emptying times are not exceeded. The accuracy achieved depends exclusively on the accuracy of the absolute volume of the containers G 1  and G 2  (or the accuracy of the respective filling volumes). 
     For volume accuracy of the containers used, with the system and method for absolute exchanged volumes, an accuracy of 0.05% and therefore volume differences between the bleed and feed solution of less than 0.1% are achieved. 
     In the embodiment shown in  FIG. 1 , the filling pipe and the intake pipe for the first interim container G 1  are the same pipe, and the feed pumps P 2  and P 3  are switched off, for increasing the accuracy of filling the first interim container G 1  for the feed solution with the pump P 1 , and emptying the second interim container G 2  for the bleed solution with the pump P 4 . If the pumps P 2  and P 1  are switched on at the same time, the flow rate (due to the increased pressure from the pump) would vary greatly from P 2 . This would lead to a greater inaccuracy. The same applies to the second interim container G 2 . 
     The device and method in  FIG. 1  work quasi-continuously. The concentration course in  FIG. 2  is still slightly saw-toothed. By comparison of the measured and calculated volume flows, and calculation of the correction factors of the pumps P 2  and P 3  in each cycle, an extraordinarily high accuracy, and therefore reliability of the method, is achieved. 
     A complete, continuously working bleed and feed system is shown in  FIG. 3 . Here the pipes and AnL are used separately. This also allows the bleed and feed pumps P 2  and P 3  to continue during the filling of the first interim container G 1  and the emptying of the second interim container G 2 . Through this, that even after the decrease of sensor S 1 , a sufficient volume of the feed solution to be pumped into the process tank PT is available, the pump P 2  delivers constant feed solution into the process tank PT, therefore also in contrast to  FIG. 1 , if the interim container G 1  is filled short term from T 1  with feed solution (cf.  FIG. 4 ). Correspondingly, bleed solution is continuously pumped by the pump P 3  out of the process tank PT, also in the period in which bleed solution is pumped by pump  4  out of the interim container G 2  into the tank T 2  at a higher flow rate. Once the flow of the feed solution into the process tank PT and the flow of the bleed solution out of the process tank are constant, since the pumps P 2  and P 3  are not switched off, and therefore there is no down time, the concentration in the process tank is constant in terms of time, and the bleed and feed process works continuously. 
     Also in this embodiment, the process control computer PR gathers the delivered volumes and generates the correction factors. Through this, the constancy of the concentration in the process tank PT can be further increased, without influencing the accuracy of the volume difference and the volumes exchanged. 
     In the context of the present invention, furthermore, tolerance-related inaccuracies can be reduced, as is shown as an example in  FIG. 5 . 
     The filling quantity for filling the first interim container G 1  and for emptying the second interim container G 2  can vary according to the pumps (P 1 , P 4 ) and valves (V 1 , V 4 ) used. For example, the first interim container G 1  can be overfilled, if the pump P 1  is not immediately switched off when the maximal position of the sensor S 2  is reached, since the flow rate of pump P 1  into the interim container G 1  is high. In this case, the volume of feed solution pumped into the first interim container G 1  ‘overshoots’ the calibrated volume V G1 . 
     Equally, a reduction of the volume V G2  of the bleed solution can occur, since on reaching the minimal position of the sensor S 3 , the fast pump P 4  is not immediately switched off. Since the emptying of the fist interim container G 1  is done slowly with the pump P 2 , also the filling of the second interim container G 2  with P 3 , the process control computer PR in this variant uses the sensor signals (S 1 , S 2 , S 3  and S 4 ) for calculating the correction factors, whereby a very high accuracy can be achieved. 
     These inaccuracies described as examples, and all others, whenever and wherever they come from, are corrected in the next cycle. The requirement is simply that G 1  and G 2  are not completely empty (the following pumps draw air) and G 1 /G 2  do not overflow. 
     During a feed cycle, the calibrated volume V G1  of the interim container G 1  is dispensed over the time period t iG1 . Furthermore, in the time period t iG1 , an additional volume is dispensed, which is calculated from the integration of the delivery volume of the pump P 2  by the integration time t iG1 . t iG1  is the time interval between the failing edge of the sensor (S 1 ) and the failing edge of the sensor S 2 . 
     In the same way, the volume of the bleed cycle is calculated from the calibrated volume V G2  of the second interim container G 2  and the additional delivery volumes integrated by t iG2 . Due to these improvements, the system is less vulnerable to tolerances which develop in production and while the system is in operation. In  FIG. 6 , the block diagram of regulation and control of pumps P 2  and P 3  are shown for the variants according to  FIG. 5 . This shows one of several implementation possibilities. 
     The meaning of individual formulas and parameters in  FIG. 6  are as follows: 
     
       
         
           
             
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         K 1  correction factor for pump P 2   
         V G1  calibrated volume of G 1  (actual volume) 
         ∫ t     ti   Q 2 (t)dt the nominal volume in the first interim container G 1   
         t G1  time interval between the failing edge of S 2  and the failing edge of S 1  (see  FIGS. 5 and 6 ). 
         Q 1 (t) volume flow of pump  2  to time point t 
         V k1 =∫ t     C1     +t     iC1   Q s (t)dt+V 1k-1 −V G1 −∫ t     iC1   Q 1 (t)dt 
         V k1  volume by which the next cycle must be corrected 
         ∫ t     C1     +t     iC1   Qs(t)dt nominal volume 
         V 1k-1  correction volume from last cycle 
         V G1  calibrated volume of G 1  (actual volume) 
         ∫ t     iC1   Q 1 (t)dt volume which is filled by the calibrated filling level 
         t iG1  time interval between failing edge of S 1  and failing edge of S 2  (see  FIG. 5 ) 
         Q k1 =V k1 /t k    
         Q k1  volume flow (constant during t k ), which is necessary to correct the volume V k1    
         t k  time in which the volume V k1  should be corrected (a short time is chosen so that it can be compared as quickly as possible with V k1 ) 
       
    
     For pump  3 , bleed is the same process as in pump  2  feed, and shown in  FIG. 6 . 
     Enhancement with Subsequent Dispensing 
     There are applications, in which decomposition products or accumulations of materials develop, which can only be diluted by a bleed and feed system, but despite this, cannot be kept constant with a feed solution of all material concentrations. In these cases, individual substances are added to the process tank PT according to individual use. 
     A schematic example is shown in  FIG. 7 , in which the substances A, B and C are added by each pump P 5 , P 6  and P 7 , controlled by PR. The result of this, is that on addition of A, B or C or in any respective combination of substances, the volume flow of the feed solution must be reduced, so as not to upset the balance of inflow and outflow of the process tank PT. It is also possible that the volume flow of the bleed solution will be raised accordingly. Which system gives the best results always depends on the composition and behaviour of the chemicals. 
     Enhancement with an Analysis System 
     The bleed and feed solutions described here are controlled externally, mostly by production throughput. In many cases, this leads to good results and to a relatively long lifespan of the baths. A closed-loop control can be achieved with the addition of an analytical system to the bleed and feed system. The analysis system must be able to determine the individual material concentrations, which are important for the production results. 
     A possible variant of a bleed and feed device with a coupled analysis system AS is shown in  FIG. 8 . The analysis system AS in  FIG. 8  analyses in each case, when the feed solution is dispensed into T 1 , when this is changed, or T 1  is replaced as a whole. The necessary volume flow Q is calculated for the bleed and feed system in dependence upon the material concentrations. Therefore a feed solution, which does not exactly correspond to the theoretical concentration, can be used. Accordingly, the volume flows for a predetermined production throughput are corrected in the process control computer. 
     During production, material concentrations in the process tank PT are regularly determined by using the analysis system AS. According to the results, Q is adapted for the bleed and feed system, and, if necessary, the additional components such as for example A, B and C are subsequently dispensed, in order to keep the material concentrations in the process tank PT as close as possible to the nominal value. The bleed tank T 2  in  FIG. 8  is analysed at regular intervals, in order to check the efficiency of the system. 
     Enhancement with a Processing System 
     A closed circuit results when a bleed and feed system with an analytical system is also coupled with a processing system, as shown in  FIG. 9 . This considerably reduces waste generated by the production, and also reduces production costs. 
     Up to now, systems are only known in which the bleed solution is prepared in a batch process, with the bleed and feed solutions having to be transported. Transport can be avoided with this integrated system. Environmental damage is reduced by the absence of transport, and equally so is the risk of environmental pollution caused by an accident during transportation. The total costs are also further reduced by enhancement with a processing system. 
     The invention is described in more detail by means of the following example. 
     Example of an Integrated Processing System 
     In production of semiconductors, copper is deposited on wafers. The copper bath typically contains copper sulphate, sulphuric acid, chloride and several organic bonds. In the bleed solution of a bath of this type, the decomposition products of the organic bonds are the limiting factor for the lifespan of a bath of this type. The organic bonds can be completely broken down by UV oxidation and/or chemical means in a processing system. 
     After cleaning, the organic materials are again added to the feed tank T 1  (as shown in  FIG. 9  as A, B and C and valve V 6 ). Typically, additives are also used in order to keep the nominal concentrations constant in the process tank PT. This is also done by the pumps of A, B and C and valve V 5 . 
     This type of processing can also be used for other chemical production processes. Different techniques can be used such as filtration, electrolysis, preparative HPLC and others.