Patent Publication Number: US-2007108225-A1

Title: Liquid dispensing system

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
      This application is a continuation of U.S. patent application Ser. No. 10/988,802, filed on Nov. 15, 2004, for “Liquid Dispensing System” by Kevin T. O&#39;Dougherty. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to the dispensing and delivery of liquids. In particular, the present invention relates to a system for dispensing liquid that allows for easy control of the volume and speed of liquid dispensed from the same input liquid source.  
      Certain manufacturing processes require the use of liquid chemicals such as acids, solvents, bases, photoresists, dopants, inorganic solutions, organic solutions, biological solutions, pharmaceuticals, and radioactive chemicals. In many manufacturing process applications, fluid containers are employed as a source of process liquids for liquid delivery systems. Typically, the fluid containers are fabricated and filled at locations remote from the end-use facility. After filling the containers at a filling facility, the containers are typically shipped to the end-use facility, such as for use in a manufacturing process.  
      At the end-use facility, the fluid container is either incorporated directly into a liquid dispensing system or the liquid from the fluid container is emptied directly into a reservoir connected to the liquid delivery system. Liquid dispensing systems allow alternative containers to be used to deliver liquid chemicals to a manufacturing process at a specified time. These process liquids are usually dispensed from the fluid containers by special dispensing pumps.  
      In the manufacture of thin film transistor flat panel displays, the dispensing and delivery of many expensive chemicals is required. These chemicals include photoresist, color filter material, black matrix material, and so on. These chemicals are typically dispensed in the manufacturing process for spin coating, slit/extrusion coating, or a combination of the two. Systems that dispense these chemicals must be flexible to allow for different amounts of chemical and different dispense speeds to be realized with the same chemical input. Systems incapable of serving this function necessitate redundant dispense equipment, thereby increasing the overall cost of the system.  
      Most current dispensing systems that allow for different amounts of chemical and different dispense speeds to be realized with the same input liquid source employ dispense pumps in the dispense train. These pumps are not only expensive, but also are known to contribute to contamination in the form of bellows and diaphragm shedding, as well as shedding from wear on the pump check valves. Some systems attempt to engineer around the expensive pumps with an arrangement wherein the liquid is forced out of the container with a drive gas. However, the accuracy and flexibility of the amount and speed of chemical dispensed are difficult to maintain. Further, the drive gas can be forced into the dispensed liquid, thereby causing microbubbles to form in the liquid. The presence of microbubbles in the deposited liquids may cause defects in the deposited layer or subsequent deposited layers.  
      Another conventional approach to varying the amount and speed of chemical dispensed from the same input liquid source involves using a flow control device in the dispense train. In this type of system, flow rate is controlled via a closed feedback loop, and the volume of the dispense is controlled by the amount of time the liquid is dispensed. However, some dispensing systems using flow control devices have poor stability when a certain amount of liquid must be dispensed in a short period of time. Also, flow control devices are very expensive, thus adding to the overall cost of the dispense system.  
      Thus, there is a need for a low-cost liquid dispensing system that eliminates the use of pumps and allows for easy control of the amount and speed of fluid dispensed from the same input fluid source.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention is a control system employed for dispensing liquid to a process from a container including an outer container and an inner container via a flow passage. The inner container is made of a flexible material and occupied by the liquid so that pressurized fluid in a compression space between the outer container and the inner container forces liquid out of the inner container to the manufacturing process via the flow passage. A pressure sensor is positioned to sense pressure in the flow passage. A controller that is responsive to the pressure sensor controls flow of the liquid in the flow passage by controlling the pressure of the pressurized fluid in the compression space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic of a liquid dispensing system according to one embodiment of the present invention for dispensing liquid to a manufacturing process. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a schematic of liquid dispensing system  10  according to one embodiment of the present invention for dispensing liquid  12  to manufacturing process  13  from container  14 . Container  14  includes flexible inner container  20  and rigid outer container  22 . System  10  further includes pressurized gas supply  30 , pressurized gas passage  32 , pressure regulator  34 , block valves  36   a  and  36   b , pressure release passage  37 , pressure release valves  38   a  and  38   b , pressure release drain  39 , flow passage  40 , filter  42 , pressure transducer  44 , stop/suckback valve  46 , and controller  50 .  
      Outer container  22  provides the mechanical support and protection required by flexible inner container  20  (e.g., a flexible polymeric bag or liner) during filling, transport, handling, and dispensing. Outer container  22  is typically constructed of metal, although other materials, including plastic materials, may also be used, depending upon government regulatory specifications for handling of the particular liquid to be contained within container  14 . Container  14  is, for example, a container as shown in U.S. Pat. No. 5,335,821 to Osgar issued on Aug. 9, 1994, which is herein incorporated by reference.  
      Pressurized gas supply  30  is connected to compression space  31  (i.e., the space between inner walls of outer container  22  and outer surfaces of the inner container  20 ) via pressurized gas passage  32 . Pressure regulator  34  is connected along pressurized gas passage  32  to regulate the pressure that is provided to block valves  36   a  and  36   b . Block valves  36   a  and  36   b , which in one embodiment are coarse and fine adjust block valves, respectively, are connected in parallel along pressurized gas passage  32  to modulate the pressure from pressurized gas supply  30  that is provided to pressurized gas passage  32 . The use of multiple valves allows for fine-tuning of the air pressure in compression space  31 . It will be appreciated that while two block valves  36   a  and  36   b  are shown, block valves  36   a  and  36   b  may be substituted by any device capable of adjusting pressure to compression space  31  from pressurized gas supply  30  (e.g., a single block valve).  
      The interior of inner container  20  is in fluid communication with manufacturing process  13  via flow passage  40 . Flow passage  40  is typically provided in a probe that is insertable through a port of the container and into inner container  20  to provide fluid communication between liquid  12  and manufacturing process  13 . Optional filter  42  is shown connected across flow passage  40 . Alternatively, filter  42  may be integrated into container  14 . Pressure transducer  44  is connected along flow passage  40  downstream from filter  42 . Stop/suckback valve  46  is connected at an end of flow passage  40  proximate to manufacturing process  13 .  
      Controller  50 , typically a microprocessor-based controller, is connected to block valves  36   a  and  36   b , pressure release valves  38   a  and  38   b , pressure transducer  44 , and stop/suckback valve  46 . Controller  50  receives signals from pressure transducer  44  and provides signals to block valves  36   a  and  36   b , pressure release valves  38   a  and  38   b , and stop/suckback valve  46 .  
      In one embodiment of system  10 , pressure regulator  34 , block valves  36   a  and  36   b , pressure release valves  38   a  and  38   b , filter  42 , pressure transducer  44 , stop/suckback valve  46 , and interfaces to pressurized gas supply  30  and controller  50  are provided in a single package attachable to container  14 . The package including the system components listed can then simply be connected to container  14 , pressurized gas supply  30 , controller  50 , and a power supply (not shown) to begin dispensing liquid from container  14  to manufacturing process  13 . In conventional systems that include pumps and flow control devices to control the flow of liquid to the manufacturing process, this type of simple connectivity is not possible since these components are not readily integrated into a single package. Furthermore, even if pumps or flow control devices were readily integrated into a single package, the production of many such packages would be very expensive due to the high cost of pumps and flow control devices. It should be noted that alternatively any of pressure regulator  34 , block valves  36   a  and  36   b , filter  42 , pressure transducer  44 , and stop/suckback valve  46  may also be provided individually (that is, not integrated in a single package) at the end-use facility.  
      In operation, controller  50  receives a dispense recipe as an input (typically input by a user of system  10 ) that includes a recipe amount of liquid to be dispensed to the manufacturing process and a dispense duration within which the recipe amount of liquid must be dispensed to the manufacturing process. For example, dispense recipe may command system  10  to dispense 30 mL of liquid  12  to manufacturing process  13  in one and a half seconds. As another example, dispense recipe may command system  10  to dispense the 30 mL of liquid  12  to manufacturing process  13  in twelve seconds. The dispense recipe also includes other information about the liquid (e.g., viscosity, density, etc.) and the manufacturing process (e.g., ambient temperature of the process) that controller  50  takes into account during the dispensing process. Controller  50  subsequently provides a signal to stop/suckback valve  46  to open a fluidic path between container  14  and manufacturing process  13 . If block valves  36   a  and  36   b  are closed, controller  50  also provides a signal to block valves  36   a  and  36   b  that causes block valves  36   a  and/or  36   b  to open. This causes pressurized gas to flow from pressurized gas supply  30  to compression space  31  via pressurized gas passage  32 . In one embodiment, pressurized air supply  30  has a pressure between about 60 and 100 pounds per square inch gauge (psig).  
      The pressurized gas, preferably compressed air or nitrogen, is supplied to compression space  31  by pressurized gas supply  30  to force liquid  12  through filter  42 , pressure transducer  44 , and stop/suckback valve  46  via flow passage  40 . As liquid  12  is dispensed from inner container  20  of container  14 , air is permitted to enter compression space  31 , thereby collapsing flexible inner container  20 . Optionally, an additional gas passage and pressure regulator (not shown) connected between pressurized gas supply  30  and compression space  31  could be supplied to provide a predetermined constant pressure to compression space  31 . This additional connection to pressurized air supply  30  would allow system  10  to reach the desired pressure to compression space  31  more rapidly. It should also be noted that while inner container  20  is collapsed with pressurized gas in this embodiment, any means capable of collapsing inner container  20  to force liquid  12  through flow passage  40  may be used, including hydraulic or mechanical based devices.  
      When liquid  12  flows through flow passage  40 , pressure transducer  44  senses the pressure of liquid  12  flowing through flow passage  40 . According to Poiseuille&#39;s law (also known as the Hagen-Poiseuille law), the pressure in flow passage  40  at pressure transducer  44  is proportional to the flow rate in flow passage  40 . The pressure in flow passage  40  is preferably measured downstream from filter  42  such that dispense accuracy is not affected by filter restriction due to use and impurity retention of filter  42 . The pressure sensed by pressure transducer  44  is provided to controller  50 . Controller  50  then compares the pressure sensed by pressure transducer  44  to the pressure required to dispense liquid  12  to manufacturing process  13  within the specifications of the dispense recipe (i.e., time of dispense, amount of liquid  12  to dispense to manufacturing process  13 , etc.). If necessary, controller  50  then adjusts the pressure from pressurized gas source  30  to compression space  31  by modulating block valves  36   a  and  36   b  to increase or reduce the pressure from pressurized gas source  30  at compression space  31 .  
      After the pressure to compression space  31  has been adjusted, the pressure applied to inner container  20  is likewise adjusted, thereby causing a change in flow rate through flow passage  40 . This change in flow rate is measured as a corresponding pressure change through flow passage  40  by pressure transducer  44 . This closed loop control of the flow rate of liquid  12  to manufacturing process  13  allows system  10  to provide a liquid dispense according to the specifications of the dispense recipe. Furthermore, the ability to vary the flow rate of liquid  12  through flow passage  40  by adjusting the pressure to compression space  31  permits different dispensing recipes to be carried out from the same liquid source.  
      In one embodiment, block valves  36   a  and  36   b  are high speed/high cycle life DC solenoid valves. When controller  50  receives a signal from pressure transducer  44 , controller  50  uses a control algorithm to produce a drive signal that controls block valves  36   a  and  36   b  based on dispense recipe, manufacturing process, and current pressure parameters. In one embodiment, the drive signals used to control block valves  36   a  and  36   b  are pulse width modulated signals. The pulse width modulation carrier frequency is selected based on the response time of the solenoid valves. Controller  50  includes a proportional feedback component to calculate an error signal based on the difference between the current pressure at pressure transducer  44  and the pressure necessary to meet the flow rate specifications of the dispense recipe. This error signal is used by controller  50  to modulate the pulse width of the drive signal provided to block valves  36   a  and  36   b . This results in an adjustment of the pressure supplied to compression space  31 . In another embodiment, controller  50  additionally includes derivative and integral feedback components to provide error signals related to the rate of change in pressure over time at pressure transducer  44  and the variation of the rate of change in the pressure signal over time, respectively. These error signals are also used by controller  50  to modulate the drive signal that controls block valves  36   a  and  36   b.    
      During dispensing, controller  50  controls pressure release valves  38   a  and  38   b  as necessary to prevent overpressurization of compression space  31 . In one embodiment, pressure release valves  38   a  and  38   b  are high speed/high cycle life DC solenoid valves that are controlled by controller  50  with pulse width modulated signals. When controller  50  receives a signal from pressure transducer  44 , controller  50  determines whether too much pressure has been supplied to compression space  31 . If controller  50  determines that the pressure is too high in compression space  31 , controller  50  opens pressure release valves  38   a  and  38   b , as necessary to reduce the pressure in compression space  31  to an appropriate level. In one embodiment, pressure release valves  38   a  and  38   b  are coarse and fine adjust block valves, respectively, to allow for fine-tuning of the air pressure in compression space  31 . This provides a fluidic path between compression space  31  and pressure release drain  39  via pressure release passage  37 , thereby reducing the pressure in compression space  31 . Pressure transducer  44  continuously provides a signal to controller  50  related to the pressure in flow passage  40  as the pressure is reduced in compression space  31 . When controller  50  determines that the pressure in compression space  31  has reached an appropriate level, controller  50  closes pressure release valves  38   a  and  38   b . Optionally, system  10  may additionally include another pressure release passage (not shown) connected directly to pressure release drain  39  which, when opened, facilitates rapid release of pressure in compression space  31 .  
      When the amount of liquid  12  dispensed to manufacturing process  13  corresponds with the dispense recipe specifications, system  10  terminates dispensing of liquid  12  to manufacturing process  13 . Controller  50  sends a signal to stop/suckback valve  46  to terminate the fluidic connection between the interior of inner container  20  and manufacturing process  13 . Stop/suckback valve  46  then draws or sucks any liquid  12  that is between stop/suckback valve  46  and manufacturing process  13  back into flow passage  40 . This suckback procedure prevents extra liquid  12  from dripping or drooling from flow passage  40  to manufacturing process  13  after the dispense recipe specifications have been met.  
      Various modifications can be made to the liquid dispensing system heretofore described without departing from the spirit and scope of the present invention. For example, with certain liquid chemicals (e.g., color filter chemicals used to make thin film transistor flat panel displays), it is sometimes desirable to transport and store liquid  12  with a headspace gas in inner container  20  to prevent decay of liquid  12 . This headspace gas must be removed prior to dispensing liquid  12  to manufacturing process  13 . In order to accomplish this, a headspace gas removal system could be incorporated into system  10 , such as that described in U.S. patent application Ser. No. 10/823,127, filed on Mar. 13, 2004, entitled “Liquid Dispensing Method and System with Headspace Gas Removal” by K. O&#39;Dougherty, R. Oberg, J. Menning, G. Eiden, and D. Grant, which is herein incorporated by reference. In addition, container  14  may be filled so as to provide zero headspace in inner container  20  using the method and system described in U.S. Pat. App. No. 2003/0205285, filed on Nov. 6, 2003, entitled “Apparatus and Method for Minimizing the Generation of Particles in Ultrapure Liquids” by W. Kelly and D. Chilcote, which is also herein incorporated by reference. Furthermore, system  10  is expandable to allow for multiple dispense points from a single container  14 .  
      The liquid dispensing system of the present invention offers several advantages over conventional dispensing systems. For example, because system  10  uses no pumps in the dispense train, liquid  12  will be free of contamination common in conventional systems caused by deterioration of pump components. In addition, liquid  12  is shielded by inner container  20  from the pressurized gas that forces liquid  12  through flow passage  40 . This prevents gas from being forced into liquid  12  during the dispensing process, thereby preventing the formation of deleterious microbubbles in liquid  12 . Plus, the components of system  10  are relatively inexpensive compared to pumps and other flow control devices, thus reducing the cost of the overall dispensing system. Furthermore, the components of system  10  can easily be integrated into a single, transportable package, which allows for quick and simple connection to the manufacturing process at the end-use facility.  
      In summary, current dispensing systems that allow for different amounts of chemical and different dispense speeds to be realized with the same input liquid source employ dispense pumps or flow control devices in the dispense train. However, these components are expensive, are known to contribute to contamination of the liquid, and can have poor stability. The liquid dispensing system of the present invention addresses these and other drawbacks of conventional liquid dispensing systems. The liquid is dispensed to a manufacturing process from a container including an outer container and a flexible inner container occupied by the liquid. The system includes a flow passage to provide fluid communication between an interior of the inner container and the manufacturing process. A pressurized fluid source is provided that is in fluid communication with a space between inner walls of the outer container and the inner container. The pressurized fluid source causes fluid under pressure to flow into the space between the inner walls of the outer container and the inner container to force liquid out of the inner container to the manufacturing process via the flow passage. A pressure sensor is positioned to sense pressure in the flow passage. A controller responsive to the pressure sensor controls the pressure in the flow passage by modulating the pressure from the pressurized fluid source.  
      Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.