Abstract:
The present invention provides methods and apparatus combining a pressure vessel and a centrifugal pump to accurately and efficiently control pressure and flow rate of liquid in a liquid dispense system. The present invention particularly relates to the accurate and efficient control of pressure and flow rate of liquids, such as high purity chemicals or slurries used in semiconductor manufacturing processes.

Description:
FIELD OF THE INVENTION  
       [0001]     The present application provides methods and apparatus for the delivery of liquids under conditions that require highly accurate control of pressure or flow rate. In particular, the present invention provides methods and apparatus for the delivery of high purity chemicals or slurries to one or more points of use in a semiconductor manufacturing process, wherein the flow rate of the chemical or slurry is provided at a constant flow rate to the points of use.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is often desirable to precisely control the amount of liquid provided to an end point of a liquid dispensing system. Further, it is important that the amount of liquid provided is as constant as possible to avoid spiking that can have deleterious effects. This is particularly true for semiconductor manufacturing processes where the amount of liquid provided can greatly affect the process, such as layer formation, etching, cleaning, etc. Variations in pressure can lead to non-repeatability and ultimately a loss in yield. Flow control is also important. For certain processes, such as semiconductor processes requiring slurries, it is important to maintain the flow rate at a velocity necessary to keep particles suspended in the slurry. Alternatively, for high purity chemical applications, maintaining consistent flow rate is important to assure optimum filtration. Changes in flow rate can also affect the pressure in the distribution system, such as by frictional losses (e.g. headloss) in piping or filtration cartridges.  
         [0003]     It is therefore desirable to provide a precise, controllable, constant flow rate of liquid to the points of use or end point of the dispensing system. However, this can be difficult to achieve for a number of reasons, including, variations in demand, pressure changes in the distribution system during operation, pressure changes caused by filter clogging, pump cycle effects, and others. To more fully explain the problems that must be overcome,  FIG. 1  is provided to illustrate a basic liquid dispensing system as known in the prior art.  
         [0004]      FIG. 1  shows a basic system  100 , including a liquid dispense tank  10 , a pump  20 , and a point of use  30 . In the system  100 , the pump delivers liquid from tank  10 , to the point of use  30 . The tank  10  is typically a standard vented tank that may be refilled with liquid as needed from a liquid source  40 . The pump  20  may be any standard type of pump, such as a positive displacement pump or an impeller pump. However, more recently, centrifugal pumps have been used for bulk chemical and slurry applications. This trend is even more recent in the semiconductor industry where because of purity concerns, only a limited number of centrifugal pumps have been accepted for use.  
         [0005]     Centrifugal pumps are good at maintaining stable pressures for small liquid demands. However, large consumption demands or disruptions in the distribution system, e.g. charging an empty filter housing, can cause flow transients that significantly reduce the output pressure of the centrifugal pump and therefore significantly effect the pressure in the distribution system. Further, centrifugal pumps demand a high amount of electrical power and have limitations on discharge pressure. Reaching higher pressures requires more electrical power and centrifugal pumps running at the high RPMs needed for high pressure operation, can introduce heat into the system that may negatively impact some processes.  
         [0006]     While only one point of use  30 , is shown in  FIG. 1 , it will be recognized by those skilled in the art, that multiple points of use could be provided with liquid from the same dispensing system  100 . However, as will also be recognized, additional points of use add to the complexity of the system and make it harder to maintain system pressure and flow rate. As will be noted in  FIG. 1 , excess liquid is provided through the distribution system  100 , to help stabilize the flow rate and pressure at the point of use  30 . In particular, liquid is delivered out of the tank  107  flows through the system  100 , is provided in the required amount to the point of use  30 , and any excess liquid flows back to the tank  10  for reuse. To better control system pressure or flow rate, a feed back loop may be provided. In particular, as shown in  FIG. 1 , a sensor  50 , such as a pressure sensor or a flow meter, provides information indicative of the flow rate, which can be used to control the speed of the pump  20 , or to provide back pressure control for the system  100 , through operation of a flow restrictor  60  associated with the tank  10 . These components also add complexity to the system.  
         [0007]     As noted above, the tank  10  is normally a standard vented tank. However, pressure vessels have also been used to provide more stable pressure control to the distribution system. There are many variations on pressure vessel dispense systems, all of which have certain disadvantages. For example, multiple pressure vessels that operate in sequence can provide the most stable pressure for the system, but suffer from system complexity because of the need to continually pressurize, empty, vent and refill as liquid is circulated through the system. When a single pressure vessel is used, the liquid returning to the vessel must be first sent to a vessel at a lower pressure than is required for the dispense vessel and then pumped back into the dispense vessel. When liquid demand is low, significant energy is still consumed because of the necessity of maintaining the re-circulating flow.  
         [0008]     There remains a need in the art to overcome the problems noted above.  
       SUMMARY OF THE INVENTION  
       [0009]     The present application provides methods and apparatus for the delivery of liquids under conditions that require highly accurate control of pressure or flow rate. In particular, the present invention provides methods and apparatus for the delivery of high purity chemicals or slurries to one or more points of use in a semiconductor manufacturing process, wherein the flow rate of the chemical or slurry is provided at a constant flow rate to the points of use.  
         [0010]     The objectives of the present invention are accomplished by combining a pressure vessel and a centrifugal pump within the same distribution system. By using both a pressure vessel and a centrifugal pump together, the advantages provided by each component can be optimized and the overall performance of the system can be enhanced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic view of a basic system as known in the prior art.  
         [0012]      FIG. 2  is a schematic view of a basic system according to one embodiment of the present invention.  
         [0013]      FIG. 3  is a schematic view of a further embodiment of the present invention showing optional components and arrangements of the system.  
         [0014]      FIG. 4  is a schematic view of a further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
         [0016]      FIG. 2  is a schematic view of a basic system according to one embodiment of the present invention. In particular,  FIG. 2  shows a liquid distribution system  200 , comprising a pressure vessel  210  that can be refilled from a liquid source  240 , a centrifugal pump  220 , and a point of use  230 . While only a single point of use  230  is shown, it will be recognized by those skilled in the art, that multiple points of use may be supplied with liquid using the same distribution system  200 . Also shown is a pressure regulating means  250  that can be used to establish and maintain the appropriate pressure within pressure vessel  210 . For example, regulating means  250  may comprise a nitrogen gas feed. The centrifugal pump  220  may be any corrosion resistant centrifugal pump such as those pumps manufactured by Levitronix®, LLC.  
         [0017]     In operation, liquid is pumped through the system  200 , by the centrifugal pump  220 . Liquid is delivered out of the pressure vessel  210 , and provided to the point of use  230 . Any excess liquid is returned to the pressure vessel  210 . Preferably, the return line would be submerged below the liquid level in the pressure vessel  210 . Pressure within the system  200 , is maintained by establishing the appropriate pressure within the pressure vessel  210 , for example by pressurization using regulating means  250 . The speed for the centrifugal pump  220  is also set appropriately to maintain the system  200  pressure at a desired level.  
         [0018]     By using the pressure vessel  210  in conjunction with the centrifugal pump  220 , significant advantages are achieved. In particular, by using a pressurized vessel  210 , the centrifugal pump  220  can operate at lower speeds and still produce the required system  200  pressure. In this way, the system  200  according to the present invention requires much less energy than the systems of the prior art that utilize a standard vented tank. Further, by using the pressure vessel  210  and centrifugal pump  220 , higher system pressure can be achieved than if a vented tank is used.  
         [0019]     A further advantage of the present invention is that the regulated pressure of pressure vessel  220  serves to dampen pressure fluctuations during transient periods of operation. For example, the higher the pressure there is in pressure vessel  210 , the more it will limit return flow, thus reducing frictional headloss. This provides a stabilizing effect on the pressure throughout the system  200 .  
         [0020]      FIG. 3  is a schematic view of a further embodiment of the present invention showing optional components and arrangements of the system. In particular,  FIG. 3  shows a liquid distribution system  300 , comprising a pressure vessel  310  that can be refilled from a liquid source  340 , a centrifugal pump  320 , and a point of use  330 . While only a single point of use  330  is shown, it will be recognized by those skilled in the art, that multiple points of use may be supplied with liquid using the same distribution system  300 . Also shown is a pressure regulating means  350  that can be used to establish and maintain the appropriate pressure within pressure vessel  310 . For example, regulating means  350  may comprise a nitrogen gas feed. Additional components are also included in the system  300 , to provide for loop feedback control of the pressure and flow rate. A sensor  360  is provided to measure a condition of the liquid in the system  300 . For example the sensor  360  may be a pressure sensor that measures the pressure of the liquid, or may be a flow meter to measure flow rate of the liquid. The sensor  360  provides a signal representing the measurement to a controller  370  that then sends a signal to other components of the system  300  to more accurately control pressure or flow rate within the system  300 . For example, the controller  370  may send a signal to the pump  320  to adjust the speed of the pump  320  so that the measurement made by the sensor  360  remains constant. In other words, if the sensor  360  is a pressure sensor, then a signal representing the pressure of the liquid in the system  300  is sent to the controller  370 . Based on this measurement, the controller determines whether an adjustment is needed to maintain constant pressure in the system  300 , and if so, then sends a signal to appropriately adjust the speed of the pump  320 . If the sensor  360  is a flow meter, the speed of the pump  320  can be similarly adjusted to reduce or increase flow rate as required to maintain a constant flow rate to the point of use  330 .  
         [0021]     Alternatively, the controller  370  may send a signal to the regulating means  350  to adjust pressure in the pressure vessel  310  as required to maintain constant pressure or flow to the point of use  330 . One advantage of this alternative is that the centrifugal pump  320  can be operated at a constant speed, while the pressure of the pressure vessel  310  is adjusted to control system  300  operation.  
         [0022]     A further alternative is to have the controller  370  provide signals to both the pump  320  and the regulating means  350  to maintain constant pressure and flow rate to the point of use  330 .  
         [0023]     While  FIG. 3  includes only a single sensor  360 , the present invention also includes embodiments having more than one sensor. For example, two pressure sensors could be utilized and both would provide signals to the controller  370 . Based on these signals, the controller  370  could provide one output signal to the regulating means  350  to set pressure in the pressure vessel  310  and control pressure at the first sensor and another output signal to the pump  320  to control pump speed and control pressure at the second sensor. Other alternatives using flow meters in place of pressure sensors or combinations are also included. For example, the pressure of pressure vessel  310  could be adjusted to maintain pressure at a pressure sensor and the speed of pump  320  could be adjusted to maintain flow rate at a flow meter.  
         [0024]     Other alternatives and embodiments are included in the present invention. For example, additional centrifugal pumps could be added to the system to provide back up and redundancy for the system. In addition, multiple pressure vessels could be utilized, either for back up and redundancy or to allow liquid blending to take place in one pressure vessel while another vessel is distributing liquid through the system. Isolation valves can be added to the system to allow for servicing. In addition, pressure relief valves could be provided to protect against failure of the pressure regulating means. Humidification can also be provided if needed, for example, by humidifying the nitrogen gas stream used for pressurization.  
         [0025]      FIG. 4  is a schematic view of a further embodiment of the present invention. In particular,  FIG. 4  shows a liquid dispensing system  400 , comprising a pressure vessel  410 , that can be refilled from a liquid source  440 , such as a source drum or day tank, two centrifugal pumps  420 ,  425 , and points of use  430 . While multiple points of use  430  are shown in  FIG. 4 , it will be recognized by those skilled in the art that a single point of use could be supplied by the system  400 . The centrifugal pumps  420  and  425  are redundant, i.e. one pump acts as a back up to the other. Further included in the system  400  is a regulating means  450  to control pressure within pressure vessel  410 , a first sensor  460  that measures a condition of the liquid in the system  400  and produces a signal to control the speed of centrifugal pumps  420  or  425 , and a second sensor  470  that measures a condition of the liquid in the system  400  and produces a signal to control the pressure of the pressure vessel  410 . For example, the first sensor  460  may be a pressure sensor or a flow meter and can be utilized to control the speed of centrifugal pumps  420  or  425  in the same manner as set forth above with respect to  FIG. 3 . The second sensor  470  may also be a pressure sensor or a flow meter and can be utilized to control pressure within pressure vessel  410  in the same manner as set forth above with respect to  FIG. 3 .  
         [0026]     Alternatives for the embodiment shown in  FIG. 4  are the same as those mentioned above with respect to  FIG. 3 . In particular, additional centrifugal pumps could be added to the system to provide further back up and redundancy for the system. Multiple pressure vessels could be utilized, either for back up and redundancy or to allow liquid blending to take place in one pressure vessel while another vessel is distributing liquid through the system. In a particular embodiment, the pressure vessel may be a load cell so that liquid level in the pressure vessel can be determined at any time during operation. Isolation valves can be added to the system to allow for servicing. In addition, pressure relief valves could be provided to protect against failure of the pressure regulating means. Humidification can also be provided if needed, for example, by humidifying the nitrogen gas stream used for pressurization.  
         [0027]     The present invention provides many advantages over the prior art by combining the favorable attributes of both pressure vessels and centrifugal pumps. In particular the centrifugal pumps of the system according to the present invention can operate at lower speeds and still produce the required system pressure. Therefore the systems according to the present invention require much less energy than the systems of the prior art that utilize a standard vented tank. Further, by using a pressure vessel and centrifugal pump together system pressures can be achieved than if a vented tank is used. A further advantage of the present invention is that the pressure vessel serves to dampen pressure fluctuations during transient periods of operation and provides a stabilizing effect on the pressure throughout the system  200 .  
         [0028]     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.