Abstract:
A liquid Y-strainer having a filter which can be automatically flushed without system shutdown or easily and quickly removed for cleaning or replacement, as needed. The Y-strainer includes a conduit which is connected to a liquid flow system such as a drain system for wet scrubbers or water cooling systems used in the fabrication of semiconductors, for example. A typically conical filter housing extends from the conduit and contains a typically removable, conical filter for screening particles from the liquid conveyed through the conduit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to Y strainers used for filtering particles from effluent in a wafer scrubber or water cooling tower used in semiconductor fabrication facilities. More particularly, the present invention relates to a Y strainer having a filter which can be easily and quickly flushed or removed from the strainer for cleaning and replacement, as needed.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the fabrication process for semiconductor devices, numerous fabrication steps, as many as several hundred, must be executed on a silicon wafer in order to complete integrated circuits on the wafer. Since the processing of silicon wafers requires extreme cleanliness in the processing environment to minimize the presence of contaminating particles or films, the surface of the silicon wafer is frequently cleaned after each processing step. For instance, the wafer surface is cleaned after the deposition of a surface coating layer such as oxide or after the formation of a circuit by a processing step such as etching. A frequently-used method for cleaning the wafer surface is a wet scrubbing method.  
         [0003]     In cleaning a wafer surface by a wet scrubbing method, a wafer is rotated at a high speed, i.e., at least about 200 RPM and preferably, about 1,000 RPM, simultaneously with a jet of high-pressure deionized water sprayed on top. The water jet is normally sprayed at a pressure of about 2,000-3,000 psi. The water movement on top of the wafer surface displaces any contaminating particles that are lodged on the wafer surface.  
         [0004]     A typical conventional wet scrubber for semiconductor wafers is generally indicated by reference numeral  2  in the schematic of  FIG. 1  and includes a chamber  4  including an inlet  6  through which a wafer (not illustrated) is placed in the chamber  4  and an outlet  8  through which the wafer is removed from the chamber  4 . Multiple spray nozzles  10  are provided in the top of the chamber  4  for spraying water  12  onto the wafer inside the chamber  4 . A viewing window  14  may be provided in the chamber  4  for viewing the wafer therein. The spray water  12  is drained from a collecting receptacle  16  at the bottom of the chamber  4  through a water drain line  18 , which distributes the water through a Y-strainer  20  including a typically cylindrical filter  22 , as illustrated in  FIG. 3 . The filter  22  of the Y-strainer  20  removes particles  31  from the water, and a water return line  24  re-distributes the filtered water ultimately back to the spray nozzles  10 . Pressure monitors  21  may be provided in the water drain line  18  and water return line  24  on respective sides of the Y-strainer  20  to monitor and compare the pressure of water flowing through the water drain line  18  and water return line  24 . When the difference in water pressures in the water drain line  18  and water return line  24  as measured by the water pressure monitors  21  exceeds a predetermined value, such a pressure differential indicates that the filter  22  in the Y-strainer  20  may require cleaning or replacement due to excessive accumulation of particles in the filter  22 .  
         [0005]     As further illustrated in  FIG. 3 , the filter  22  of the conventional Y-strainer  20  is contained inside the generally cylindrical filter housing  30 , which angles from an elongated conduit  26  fitted with end flanges  28  for attachment of the Y-strainer  20  to the water drain line  18  and water return line  24 , respectively. The cylindrical filter  22  extends into the conduit  26  and catches the water flowing therethrough, such that particles  31  in the water are trapped and accumulate in the filter  22 . A cap  32  on the filter housing  30  is periodically removed to facilitate removing the particles  31  from the filter  22 .  
         [0006]     In another application, illustrated in  FIG. 2 , the conventional Y-strainer  20  is used to filter water in a water cooling system  34  including a cooling tower  36 , typically having a pair of conduits  38  for conveying processing water to a heat sink  40 . A fan  42 , powered by an electric motor  44 , draws cool air across the conduits  38  to dissipate heat from the water flowing therethrough. A water drain line  46  drains the water from the heat sink  40  and distributes the partially-cooled water through the filter  20 , wherein the Y-strainer  20  removes particles  31  from the water before the water is distributed through a heat exchanger  50  which further cools the water. Finally, a water return line  48  circulates the water back to the cooling tower  36  for a subsequent cooling cycle. Pressure monitors  47  may be provided on respective sides of the Y-strainer  20  to monitor and compare the pressure of water flowing through the water drain line  46  and water return line  48 , respectively, and thus indicate the need for cleaning or replacing the filter  22  or Y-strainer  20 .  
         [0007]     The conventional Y-strainer  20  having the conventional filter  22  suffers from several disadvantages. The filter  22  is typically fixedly mounted inside the strainer housing  30 , and this renders difficult the cleaning process for complete removal of the particles  31  from the filter  22 . Consequently, particles  31  remaining in the filter  22  tend to reduce the particle-removing efficiency of the filter  22 . This contributes to an increase in the number of contaminating particles  31  in the water re-distributed back to the spray nozzles  10  in the wet scrubber  2 , as well as reduces the efficiency of the heat exchanger  50  in the water cooling system  34 . Furthermore, the wet scrubber  2 , water cooling system  34  or other system of which the Y-strainer  20  is a part must be shut down for cleaning of the filter  22 . Because the filter  22  must typically be cleaned often, the shutdown rate for the wet scrubber  2  or the water cooling system  34  is high, and this interrupts semiconductor production and significalty increases production costs.  
         [0008]     Accordingly, a Y-strainer is needed having a filter which can be automatically flushed without requiring shutdown of the system of which the Y-strainer is a part and which filter can be easily removed from the Y-strainer for complete cleaning or for replacement thereof as needed.  
         [0009]     An object of the present invention is to provide a new and improved Y-strainer having a filter which can be flushed as needed to remove particles therefrom.  
         [0010]     Another object of the present invention is to provide a new and improved Y-strainer having a filter which can be quickly and easily removed for cleaning or replacement purposes.  
         [0011]     Still another object of the present invention is to provide a Y-strainer having a filter which may be conical in shape to facilitate quick and easy removal from and replacement in a correspondingly-shaped filter housing on the Y-strainer.  
         [0012]     Yet another object of the present invention is to provide a Y-strainer having a filter which can be flushed to remove particles therefrom without terminating operation of a wet scrubber, water cooling system or other system of which the Y-strainer is a part.  
         [0013]     A still further object of the present invention is to provide a Y-strainer which increases production and reduces production costs associated with filtering particles from water in the system.  
       SUMMARY OF THE INVENTION  
       [0014]     According to these and other objects and advantages, the present invention comprises a liquid Y-strainer having a filter which can be automatically flushed without system shutdown or easily and quickly removed for cleaning or replacement, as needed. The Y-strainer includes a conduit which is connected to a liquid flow system such as a drain system for wet scrubbers or water cooling systems used in the fabrication of semiconductors, for example. A typically conical filter housing extends from the conduit and contains a typically removable, conical filter for screening particles from the liquid conveyed through the conduit. A drain valve is provided on the end of the filter housing for periodically draining particles from the filter, as needed.  
         [0015]     The present invention further comprises a wet scrubber having a water drain line which is fitted with the Y-strainer of the present invention. Liquid pressure monitors may be provided on respective sides of the Y-strainer to monitor the pressure of the liquid flowing into and out of the Y-strainer. An increased pressure of the liquid flowing into the Y-strainer relative to the pressure of the liquid flowing out of the Y-strainer may indicate excessive accumulation of particles in the filter of the Y-strainer and thus, the need for flushing the particles from the filter. A power source and controller may be connected to the pressure monitors and the Y-strainer for automatically controlling the filter flushing operation responsive to the increased liquid pressure.  
         [0016]     The present invention further comprises a water cooling system having a water drain line which is fitted with the Y-strainer of the present invention. Liquid pressure monitors may be provided on respective sides of the Y-strainer to monitor the pressure of the liquid flowing into and out of the Y-strainer, and thus, indicate the need for flushing the particles from the filter in the Y-strainer. A power source and controller may be connected to the pressure monitors and the Y-strainer for automatically controlling the flushing operation responsive to the increased liquid pressure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The present invention will now be described, by way of example, with reference to the accompanying drawings, wherein:  
         [0018]      FIG. 1  is a schematic view illustrating a typical conventional wet scrubber for semiconductor wafers;  
         [0019]      FIG. 2  is a schematic view illustrating a typical conventional water cooling system for cooling process water in a semiconductor fabrication facility;  
         [0020]      FIG. 3  illustrates a conventional Y-strainer used in filtering water in a wet scrubber or water cooling system;  
         [0021]      FIG. 4  illustrates an illustrative embodiment of the Y-strainer of the present invention;  
         [0022]      FIG. 5  is a rear view of the filter component of the Y strainer of the present invention;  
         [0023]      FIG. 6  is a side view of the filter;  
         [0024]      FIG. 7  illustrates the Y-strainer with the filter, cap and drain valve components removed from the Y-strainer;  
         [0025]      FIG. 8  is a sectional view of an illustrative drain valve of the Y-strainer of the present invention;  
         [0026]      FIG. 9  is a bottom view of an illustrative drain valve of the Y-strainer of the present invention;  
         [0027]      FIG. 10  is a schematic view illustrating a wet scrubber in implementation of the present invention;  
         [0028]      FIG. 11  is a schematic view illustrating a water cooling system in implementation of the present invention;  
         [0029]      FIG. 12  illustrates filtering operation of the Y-strainer of the present invention during normal system operation; and  
         [0030]      FIG. 13  illustrates the filter-flushing function of the Y-strainer of the present invention, during system operation. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     The present invention has particularly beneficial utility in filtering particles from water in wet scrubbers and water cooling systems used in semiconductor fabrication processes. However, the invention is not so limited in application, and while references may be made to such wet scrubbers and water cooling systems, the invention is more generally applicable to filtering liquids in a variety of industrial and product applications.  
         [0032]     Referring to  FIGS. 4-9 , a Y-strainer of the present invention is generally indicated by reference numeral  51  and includes an elongated conduit  52 , which may be fitted with end flanges  53  on respective ends thereof for attaching the Y-strainer  51  to a water drain line or pipe and/or a water return line or pipe, as hereinafter described. Alternatively, the Y-strainer  51  may be formed integrally with or otherwise attached to the water drain line or pipe and/or the water return line or pipe. A filter housing  57 , which may be conical in shape, as illustrated, angles downwardly from the conduit  52  and communicates with a conduit interior  55  of the conduit  52 . The filter housing  57  defines a liquid intake arm  69  in the conduit  52  on one side of the filter housing  57  and a liquid outlet arm  97  in the conduit  52  on the other side of the filter housing  57 . As illustrated in  FIG. 7 , the longitudinal axis  11  of the filter housing  57  is disposed at an obtuse angle, typically from about 95 degrees to about 175 degrees, with respect to the longitudinal axis  13  of the liquid intake arm  69  and at an acute angle, typically about 5 degrees to about 85 degrees, with respect to the longitudinal axis  11  of the liquid outlet arm  97 . The filter housing  57  may be terminated by a valve mount nipple  61 .  
         [0033]     A filter  58 , which may be conical in shape, as illustrated, is removably fitted in the filter housing  57 . The filter  58  includes a frame  59 , on which is mounted a mesh  60  having mesh openings of selected size. When the filter  58  is fitted in the filter housing  57 , the wide rear end  15  of the filter  58  extends into the conduit interior  55 , as illustrated in  FIG. 4 , and engages the curved interior surface of the conduit  52 . The narrow or tapered front end  17  of the filter  58  is disposed adjacent to the valve mount nipple  61 . As further illustrated in  FIG. 7 , a cap opening  56  is provided in the conduit  52  opposite the filter housing  57 , and a cap  54  removably engages the exterior surface of the conduit  52 , as illustrated, or is hingedly attached to the conduit  52  to removably close the cap opening  56 . Accordingly, by removing the cap  54  from the conduit  52 , the filter  58  may be easily removed from and replaced in the filter housing  57  through the cap opening  56  for washing or replacement purposes, as hereinafter further described.  
         [0034]     The valve housing  63  of a drain valve  62  is mounted on the valve mount nipple  61  at the tapered end of the filter housing  57 . The drain valve  62  further includes a valve actuator  68  connected to the valve housing  63  typically through a connector  67 . As illustrated in  FIG. 8 , a drain passage  64  extends laterally through the valve housing  63 , and a valve disk  65 , provided on one end of an actuator arm  66 , is normally disposed in the drain passage  64  to prevent flow of fluid through the drain passage  64 . The opposite end of the actuator arm  66  is connected to the valve actuator  68 . Accordingly, via the actuator arm  66 , the valve actuator  68  may be operated to retract the valve disc  65  from the drain passage  64  to permit flow of liquid therethrough or extend the valve disc into the drain passage  64  to restrict flow of liquid therethrough. The valve actuator  68  may be an electric solenoid actuator, a pneumatic actuator or an oil pressure (hydraulic) actuator. It is understood that the drain valve  62  having the specific design heretofore described with respect to  FIGS. 8 and 9  serves as only one example of a valve which is suitable for draining particles from the Y-strainer  51 . Accordingly, other types of valves having any suitable alternative designs may be used instead of the drain valve  62  having the design heretofore described.  
         [0035]     Referring next to  FIG. 10 , in application the Y-strainer  51  of the present invention may be provided in a water drain line  78  of a wet scrubber  70  including a chamber  71  having an inlet  72  and an outlet  73  for a semiconductor water (not illustrated); multiple spray nozzles  74  for spraying water  75  into the chamber  71 ; and a viewing window  76 . The spray water  75  is drained from a collecting receptacle  77  at the bottom of the chamber  71  through the water drain line  78 , which distributes the water  75  through the Y-strainer  51  of the present invention. As the water flows through the conduit  52  of the Y-strainer  51 , as indicated by the arrows in  FIG. 12 , the filter  58  catches and traps particles  100  flowing with the water into the liquid intake arm  69  of the conduit  52  such that the water flowing from the conduit  52  through the liquid outlet arm  97  is essentially particle-free. A water return line  79  typically re-distributes the filtered water from the Y-strainer  51  ultimately back to the spray nozzles  74 . Over time, the particles  100  accumulate in the filter  58 , at which time the filter  58  must be flushed to remove the particles  100  therefrom. This is accomplished by opening the drain valve  62  by operation of the valve actuator  68  while continuing circulation of the water through the water drain line  78 , Y-strainer  51  and water return line  79 , respectively, of the wet scrubber  70 . Accordingly, as illustrated in  FIG. 13 , the water flows with the particles  100  previously lodged in the filter  58  from the open drain valve  62 , and the flush water  99  and particles  100  therein may be collected in a receptacle  98  or distributed through a hose (not illustrated) attached to the drain valve  62  and deposited into a suitable receptacle  98 . Flow of flush water  75  and particles  100  from the drain valve  62  is continued until the particles  100  have been essentially removed from the filter  58 , at which time the drain valve  62  is closed. It will be appreciated by those skilled in the art that the drain valve  62  may be operated to flush the particles  100  from the filter  58  during continuous operation of the wet scrubber  70 , without the need to terminate flow of water through the water drain line  78  and water return line  79 . This is apparent from a consideration of  FIG. 7 , wherein the outlet water quantity “Q2” is the same as the inlet water quantity “Q1” during normal operation of the wet scrubber  70  and filtering operation of the Y-strainer  51 . Upon opening of the drain valve  62  to flush the filter  58 , the drain water quantity “Q3” flowing from the filter housing  57  is smaller than the outlet water quantity “Q2”, and consequently, the filter-flushing operation of the Y-strainer  51  does not affect normal operation of the wet scrubber  70 .  
         [0036]     As further illustrated in  FIG. 10 , an intake pressure monitor  82  may be provided in the water drain line  78  on the intake side of the Y-strainer  51 , and an outlet pressure monitor  83  may be provided in the water return line  79  on the outlet side of the Y-strainer  51 , to monitor the pressure of water on the respective sides of the Y-strainer  51 . Accordingly, in the event that the water pressure as measured by the intake pressure monitor  82  exceeds the water pressure as measured by the outlet pressure monitor  83  by a predetermined value, typically at least about 5 psi, for example, this water pressure discrepancy indicates excessive accumulation of particles  100  in the filter  58 , and thus, a need to flush the filter  58  of the Y-strainer  51 . A power supply  80  and a controller  81  may be connected to the drain valve  62  of the Y-strainer  51 , the intake pressure monitor  82  and the outlet pressure monitor  83  to facilitate automatic flushing of the filter  58  when the water pressure as measured by the intake pressure monitor  82  exceeds the water pressure as measured by the output pressure monitor  83  by the predetermined value. In the event that the filter  58  is broken due to prolonged operation of the Y-strainer  51 , for example, the filter  58  may be easily replaced by removing the cap  54  from the conduit  52  to expose the cap opening  56 , as illustrated in  FIG. 7 ; removing the broken filter  58  from the filter housing  57  and conduit  52  through the cap opening  56 ; fitting a replacement filter  58  into the filter housing  57  through the cap opening  56 ; and replacing the cap  54  on the conduit  52  to close the cap opening  56 .  
         [0037]     Referring next to  FIG. 11 , in another application the Y-strainer  51  of the present invention may be provided in a water drain line  90  of a water cooling system  84  used for cooling hot process water in a semiconductor fabrication facility, for example. Such a water cooling system  84  may include a cooling tower  85 , typically having a pair of conduits  86  for conveying processing water to a heat sink  87 ; a fan  88 , powered by an electric motor  89 ; and the water drain line  90 , which drains the water from the heat sink  87  and distributes the partially-cooled water through the Y-strainer  51  of the present invention. The filter  58  of the Y-strainer  51  removes particles  100  from the water before the water is distributed through a heat exchanger  92  which further cools the water, in the manner heretofore described with respect to  FIG. 12 . Finally, a water return line  91  may circulate the water back to the cooling tower  85  for a subsequent cooling cycle. After particles  100  removed from the water flowing through the Y-strainer  51  have accumulated in the filter  58  after prolonged operation of the water cooling system  84 , the filter  58  may be flushed to remove the particles  100  therefrom by operation of the drain valve  62 , in the same manner as heretofore described with respect to  FIG. 13 . The filter-flushing operation can be accomplished during continuous operation of the water cooling system  84 . An intake pressure monitor  95  and an outlet pressure monitor  96  may be provided on the intake and outlet sides, respectively, of the Y-strainer  20  to monitor the pressure of water flowing through the water drain line  90  and water return line  91 , respectively, and indicate the need for cleaning or replacing the filter  58  in the event that the water pressure as measured by the intake pressure monitor  95  exceeds that measured by the outlet pressure monitor  96  by a predetermined value, typically about 5 psi, for example. A power supply  93  and a controller  94  may be connected to the drain valve  62  of the Y-strainer  51 , the intake pressure monitor  95  and the outlet pressure monitor  96  to facilitate automatic flushing of the filter  58  when the water pressure as measured by the intake pressure monitor  95  exceeds the water pressure as measured by the outlet pressure monitor  96  by the predetermined value. In the event that the filter  58  is broken due to prolonged operation of the Y-strainer  51 , for example, the filter  58  may be easily replaced by removing the cap  54  from the conduit  52  to expose the cap opening  56 , as illustrated in  FIG. 7 ; removing the broken filter  58  from the filter housing  57  and conduit  52  through the cap opening  56 ; fitting a replacement filter  58  into the filter housing  57  through the cap opening  56 ; and replacing the cap  54  on the conduit  52  to close the cap opening  56 , as heretofore described.  
         [0038]     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.  
         [0039]     Having described our invention with the particularity set forth above, we claim: