Abstract:
A method of cleaning an screen in a manufacturing process step that employs a chamber including a drain line having a screen configured and disposed in the chamber above the drain line to trap soluble materials includes detecting a build-up of soluble material on the screen, ceasing a work operation in the chamber, and initiating a screen cleaning operation. The screen cleaning operation includes closing a computer operated valve fluidly connected to the drain line to fluidly isolate a portion of the chamber, automatically introducing an amount of solvent into the chamber once the computer operated valve is closed with the amount of solvent filling the chamber and/or the drain line to fully immerse the screen, and opening the operated valve after a predetermined amount of time to empty the chamber and the drain line of solvent once the soluble materials trapped on the screen are dissolved.

Description:
BACKGROUND 
     The present invention relates to manufacturing, and more particularly, to a system and method for unclogging screens in a manufacturing process. 
     Many manufacturing processes employ systems that utilize volatile chemicals. The use of volatile chemicals further requires the use of flame arrestor screens across exhaust and or drain areas in order to prevent a flash-over. In certain cases, both exhaust and drain areas are located below the flame arrestor. In many processes, the volatile chemicals are utilized as a solvent to dissolve soluble materials. In semiconductor manufacturing for example, flammable solvents are utilized to dissolve polymeric materials. Over time, the dissolved polymeric materials accumulate on the flame arrestor clogging both the drain and the exhaust area. Clogged screens directly affect process conditions which may ultimately have a negative impact on product quality. 
     Present methods for unclogging the flame arrestor include a “brute force” method in which copious amounts of solvent are passed through the system. While effective, solvent itself is costly. Also, given the nature of the chemicals in the solvent, disposal of the solvent can also be quite costly, often times costing more than the solvent itself. As such, the brute force method not only includes a high initial cost associated with the large amounts of solvent required, but also incurs a large post cleaning/disposal cost. In addition, the brute force method can be time consuming requiring a substantial system down time. Alternatively, or in addition if the brute force method is not efficacious, the system is disassembled and the screen is physically removed for cleaning. Once removed, the screen is flushed with solvents to dislodge any trapped material. Removing the screen from the process results in substantial production down time as well as introduces a potential for improper screen replacement and/or physical damage. 
     SUMMARY 
     According to one embodiment of the present invention, a method of cleaning a screen in a manufacturing process step that employs a chamber including a drain line having a screen configured and disposed in the chamber above the drain line to trap soluble materials includes detecting a build-up of soluble material on the screen, ceasing a work operation in the chamber, and initiating a screen cleaning operation. The screen cleaning operation includes closing a computer operated valve fluidly connected to the drain line to fluidly isolate a portion of the chamber, automatically introducing an amount of solvent into the chamber once the computer operated valve is closed with the amount of solvent filling one of the chamber and the drain line to fully immerse the screen, and opening the computer operated valve after a predetermined amount of time to empty the one of the chamber and the drain line of solvent once the soluble materials trapped on the screen are dissolved. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a manufacturing process step including a chamber having a drain line provided with a screen, and a system for cleaning the screen in accordance with an exemplary embodiment; 
         FIG. 2  is a schematic diagram of the manufacturing process step of  FIG. 1  illustrating removal of soluble material from an article of manufacture in accordance with the exemplary embodiment; 
         FIG. 3  is a schematic diagram of the manufacturing process step of  FIG. 2  illustrating a build-up of soluble material on the screen in accordance with an exemplary embodiment; 
         FIG. 4  is a schematic diagram of the manufacturing process step of  FIG. 3  illustrating a cleaning operation initiated by the system for cleaning the screen in accordance with the exemplary embodiment; 
         FIG. 5  is a schematic diagram of the manufacturing process step of  FIG. 4  following the screen cleaning operation; 
         FIG. 6  is a schematic diagram of a manufacturing process step including a chamber having a drain line provided with a screen positioned in accordance with another aspect of the exemplary embodiment; and 
         FIG. 7  is a schematic block diagram of a general purpose computer configured and disposed to initiate the cleaning operation for the system for cleaning the screen. 
     
    
    
     DETAILED DESCRIPTION 
     With reference now to  FIG. 1 , a manufacturing/production process step in accordance with an exemplary embodiment is indicated generally at  2 . Process step  2  includes a process chamber  4  having a bottom wall  6 , a first sidewall  8 , and a second sidewall  10 , as well as additional sidewalls (not shown), that collectively define an interior or processing portion  12 . Process step  2 , in accordance with the exemplary embodiment, is employed in connection with the production of semiconductor wafers. Towards that end, a wafer chuck  15  is arranged within the process chamber  4 . Wafer chuck  15  includes a base or wafer support portion  16  as well as a pedestal member  17 . Pedestal member  17  elevates base/wafer support  16  above bottom wall  6 . At this point, it should be understood that while described in connection with the production of semiconductor wafers, the present invention can be employed in connection with various other manufacturing processes that employ soluble materials in a manner that will become more fully evident below. 
     Process chamber  4  includes a drain line  24  having a first end portion  26  including an opening  28  exposed to interior portion  12 . First end portion  26  extends to a second end portion  30  through an intermediate portion  32 . Second end portion  30  leads to a used solvent collection area (not shown). In the exemplary embodiment shown, a flame arrestor screen  34  is positioned across opening  28 . Of course flame arrestor screen could also be inset into opening  28 . In any event, flame arrestor screen  34  is configured and disposed to prevent flash backs within process chamber  4  that may result as a consequence of the use of volatile chemicals. 
     Process chamber  4  is also shown to include a first exhaust line  36  that extends from intermediate portion  32  of drain line  24 . More specifically, first exhaust line  36  includes a first end section  38  that is fluidly connected to intermediate portion  32  of drain line  24 . First end section  38  extends to a second end section  40  through an intermediate section  41 . Second end section  40  leads to an exhaust gas collection portion (not shown). In addition to first exhaust line  36 , process chamber  4  includes a second exhaust line  45  that is arranged above wafer support  16 . While a typical wafer processing chamber would not usually include an upper exhaust line due to the propagation of contaminants, as will become more fully evident below, second exhaust line  45  is only exposed to process chamber  4  during a cleaning operation. Second exhaust line  45  includes a first end  47  having an opening (not separately labeled) exposed to interior portion  12  above wafer chuck  15 . First end  47  extends to a second end  49  which is fluidly linked to intermediate section  41  of first exhaust line  36 . In this manner, second exhaust line  45  fluidly connects interior portion  12  with the exhaust collection point (not shown). 
     In further accordance with the exemplary embodiment, a first valve  54  is arranged on drain line  24 . More specifically, first valve  54  is arranged at a junction of first exhaust line  36  and intermediate portion  32 . A second valve  57  is arranged along second exhaust line  45  at a position upstream from second end section  40  of first exhaust line  36 . A pressure sensor  60  is arranged at first end portion  26  of drain line  24  upstream from first valve  54 . As will be discussed more fully below, pressure sensor  60  is configured to detect an amount of solvent flow through drain line  24 . Alternatively, a pressure sensor  64  can be arranged at first end section  38  of first exhaust line  36 . At this point, it should be understood that both pressure sensor  60  and pressure sensor  64  can also both be employed in connection with the invention. As will be discussed more fully below, a control system  70  is linked to first and second valves  54  and  57  as well as pressure sensors  60  and  64 . Control system  70  is configured to initiate a cleaning operation of screen  34 . In the exemplary embodiment shown, control system  70  takes the form of a programmable logic controller (PLC), however, it should be understood that control system  70  can also take the form of a general purpose computer as will become apparent more fully below. 
     As best shown in  FIG. 2 , during a processing step, soluble material  80 , such as photo resist material is removed from a semiconductor wafer supported upon wafer chuck  15 . The soluble material  80  falls from wafer support  16  and collects on bottom wall  6 . Over time, the soluble material  80  collects on screen  34  as shown in  FIG. 3 . When enough soluble material collects on screen  34 , solvent used in connection with removing the photo resist material no longer flows into drain line  24 . In order to ensure that a solvent continues to flow, controller  70  selectively initiates a screened cleaning operation. In accordance with one aspect of the exemplary embodiment, controller  70  detects a build up of soluble material  80  on screen  34 . That is, controller  70  detects a pressure differential or loss at one of pressure sensors  60  and  64 . A reduction in pressure at pressure sensor  60  can indicate a lack of solvent flow through drain line  24  indicating the presence of a build up of soluble material  80  on screen  34 . The particular degree of pressure loss can, for example, be a determination of exactly how much soluble material  80  is built up on screen  34 . 
     In any event, once controller  70  determines that a cleaning operation is required, work operations within processing chamber  4  are halted. After halting work operations within processing chamber  4 , valve  54  is closed, thus fluidly isolating second end portion  30  of drain line  24  from process chamber  4  such as shown in  FIG. 4 . Valve  54  also fluidly isolates first end section  38  of first exhaust line  36 . At the same time, valve  57  is opened exposing second exhaust line  45  to second end portion  40  of second first exhaust line  36  to facilitate a continued flow of gases from chamber  4 . At this point, an amount of solvent is introduced into process chamber  4 . The amount of solvent is added to a level  100  such that screen  34  is fully immersed. Screen  34  remains immersed in solvent for a pre-determined period to allow the build up soluble material  80  to solubalize or dissolve. Once the soluble material  80  on screen  34  has dissolved, such as shown in  FIG. 5 , valve  54  is opened and valve  57  is closed. At this point, liquid solvent is allowed to pass from process chamber  40  to second end portion  30  of drain line  24 . 
       FIG. 6 , wherein like reference numbers represent corresponding parts in the respective views, illustrates an alternative screen location. More specifically, a screen  200  is arranged within first end section  38  of first exhaust line  36 . With this arrangement, a valve  220  is arranged downstream of first exhaust line  36  within drain line  24  and a pressure sensor  230  is arranged downstream of first exhaust line  36  relative to screen  200 . In this manner, the amount of solvent required to dissolve a built up of soluble materials is even further reduced by minimizing the surface area of screen  200  to be treated. That is, the particular placement of screen  200  requires that the amount of solvent necessary to immerse screen  200  only be sufficient to fill a portion of drain line  24 . 
     The above described exemplary embodiment allow for a minimal use of solvent in order to dissolve a build up of soluble material on a filter screen arranged within a process chamber. That is, instead of a dynamic flushing of large amounts of solvent through processing chamber until a screen is clear, a minimal amount of static solvent is introduced into chamber, allowed rest until the soluble material has dissolved and then passed to the drain. In addition to using less solvent, the present invention eliminates the need to disassemble the process chamber to remove the screen for cleaning thereby reducing process down time. Process down time can be further reduced by the particular timing of the cleaning operation. That is, if experience shows that a pressure drop in the drain line of, for example 50%, requires a 1 hour soak to remove the soluble material, and a pressure drop of, for example 25% requires a 10 minute soak to remove the soluble material, the controller can programmed to initiate the cleaning operation at the lower pressure drop in order to reduce process down time. The use of less solvent allows for more frequent cleanings without an increase in cost. That is, the present invention embodiments reduce the front end or initial cost of solvent, the back end or disposal costs of the solvent and the overall process cost by reducing process down time. 
     As discussed above, the method of cleaning a filtering screen described herein can also be practiced with a general-purpose computer such as illustrated at  400  in  FIG. 7  and the method may be coded as a set of instructions on removable or hard media for use by the general-purpose computer  400 . In  FIG. 7 , computer system  400  has at least one microprocessor or central processing unit (CPU)  405 . CPU  405  is interconnected via a system bus  410  to a random access memory (RAM)  415 , a read-only memory (ROM)  420 , an input/output (I/O) adapter  425  for a connecting a removable data and/or program storage device  430  and a mass data and/or program storage device  435 , a user interface adapter  440  for connecting a keyboard  445  and a mouse  450 , a port adapter  455  for connecting a data port  460  and a display adapter  465  for connecting a display device  470 . 
     ROM  420  contains the basic operating system for computer system  400 . The operating system may alternatively reside in RAM  415  or elsewhere as is known in the art. Examples of removable data and/or program storage device  430  include magnetic media such as floppy drives and tape drives and optical media such as CD ROM drives. Examples of mass data and/or program storage device  435  include hard disk drives and non-volatile memory such as flash memory. In addition to keyboard  445  and mouse  450 , other user input devices such as trackballs, writing tablets, pressure pads, microphones, light pens and position-sensing screen displays may be connected to user interface  440 . Examples of display devices include cathode-ray tubes (CRT) and liquid crystal displays (LCD). 
     A computer program with an appropriate application interface may be created by one of skill in the art and stored on the system or a data and/or program storage device to simplify the practicing of this invention. In operation, information for or the computer program created to run the present invention is loaded on the appropriate removable data and/or program storage device  430 , fed through data port  460  or typed in using keyboard  445 . 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one ore more other features, integers, steps, operations, element components, and/or groups thereof. 
     The description of the exemplary embodiment has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated 
     The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.