Abstract:
A three-way valve is disclosed having flow ports that are co-planar and a unitary actuation stem made of a material such as a fluoropolymer that is resistant to caustic fluids commonly used in the semiconductor industry. The three way valve does not require a diaphragm, and thus occupies a smaller footprint relative to standard diaphragm-type valves. The stem is designed to accommodate valving portions or “poppets” that can be assembled by hand, without need for special tooling. The valve body may also be made of a fluoropolymer, and may be either machined or molded to form.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to valves. More particularly, this invention relates to three-way poppet style valves utilizing valve stems to control the flow of fluid between a common port and two other ports.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various types of valves are used in the semiconductor industry to transport fluids, three-way valves that switch between alternate sources of fluids. It is important that the number of potential leak paths between the source paths be kept to a minimum due to the highly caustic nature of the fluids often used in the semiconductor industry. These valves must be made of materials highly resistant to the caustic fluids. Contact with metal parts is generally to be avoided. The components which contact the fluids are typically formed of fluoropolymers such as perfluoroalkoxy (PFA), polyvinylidene (PVDF), or polytetrafluoroethylene (PTFE).  
         [0003]     Many three-way valves utilize a “diaphragm” to provide a barrier between the controlled fluids and the actuation mechanism of the valve. For purposes of this application, a “diaphragm” is hereby defined as a thin-walled, flexible sheet having a stationary outer perimeter and a central portion that flexes in a direction normal to a plane defined by the outer perimeter. The diaphragm may have concentric recesses or corrugations that reduce strain on the diaphragm when flexed. A concern with diaphragm-type valves is the life of the diaphragm. The diaphragms are preferably circular in shape to avoid stress concentration zones during flexing, and are typically three or more diameters relative to delivery conduits to reduce the strain on the diaphragm during actuation. Thus, diaphragm valves tend to have large footprints relative to the flow passageway being controlled.  
         [0004]     Three-way valves, such as the model  704  pneumatic “stack valve” produced by Entegris, Inc. of Chaska, Minn., depicted in  FIG. 1 , are preferred over the diaphragm valves in many applications. Stack valves do not require bulky diaphragms, yet retain the flexibility of pneumatic actuation. The absence of a diaphragm allows for a compact, co-planar design that reduces the footprint of the valve. However, referring to  FIG. 1 , an existing stack valve assembly  10  utilizes a valve stem assembly  12  having a core stem  14  typically made of stainless steel or polyetheretherketone (PEEK) within a sleeve  16  made of polytetrafluoroethylene (PTFE) or some other material resistant to fluid streams  18 ,  20 ,  22  being controlled. The valve stem assembly  12  operates within a flow passage  24  of a valve body  26  to control the flow of fluid between a common passage  30  and two alternating passages  32  and  34 . The sleeve  16  is press fit into contact elements or “poppets”  36  and  38  that are arranged to alternately isolate one of the two alternating passages  32  or  34  from fluid communication with the common passage  30 , depending on the direction of actuation. Also, end caps  40  and  42  are press fit into the valve body  26  to seal off the interior chambers of the stack valve assembly  10 .  
         [0005]     The  FIG. 1  design must rely on the integrity of various press fit components. A leak path  44  may develop between the sleeve and the core, with entry points at one of the press fit joints. Other leak paths  46  and  48  may develop at the press-fit joints the end caps  40  and  42 , respectively. The integrity of the various press fit seals are difficult to test prior to service.  
         [0006]     Another aspect of the configuration depicted in  FIG. 1  is the need for special tooling to accomplish the press fit assembly. It is desirable to have a stem assembly that can be easily assembled and disassembled by hand, without need for special tooling and alignment procedures associated with the press fit operation.  
         [0007]     There is a need for a three-way stack valve that does not rely on press fit components for containing the caustic fluids associated with semiconductor processes, and which can be quickly and easily assembled within the valve body portion with a minimal number of steps.  
       SUMMARY OF THE INVENTION  
       [0008]     A three-way valve having passages in a coplanar arrangement for use with caustic fluids such as those used in semiconductor processing applications is disclosed. The valve features a valve body and a unitary valve stem molded or otherwise formed from a fluoropolymer plastic material. The valve stem has two poppets, one formed integral with the valve stem, the other configured to mate with the valve stem in a “snap-on” arrangement. The snap-on arrangement eliminates the need for a press fit assembly of the wetted portions of the valve.  
         [0009]     The various embodiments of the three-way valve invention include a body portion with a central axis, a first valve seat centered about the central axis and facing downward, a second valve seat positioned above the first valve seat, also centered about the central axis and facing upward, and a connecting passage extending between the valve seats. A lower cap portion may be attached to the body portion below the first valve seat, and an upper cap portion attached to the body portion above the second valve seat. An opening, aligned with the central axis, is provided in the upper cap portion to accommodate an actuation member. A common flow passage integral to the body portion is in fluid communication with the connecting passage. A first flow passage with a first axis of flow is integral to the body portion and is in fluid communication with the connecting passage through said first valve seat. A second flow passage with a second axis of flow is integral to the central body portion and is in fluid communication with the connecting passage through the second valve seat. A valve stem having a proximate end and a distal end extends through the first valve seat, connecting passage and second valve seat, with the proximate end of the valve stem attached to the actuation member. A first contact element is integrally formed on the valve stem and oriented to allow engagement with the first valve seat. A second contact element is formed to mechanically mate with the distal end of the valve stem and is oriented for engagement with the second valve seat. The central, common, first and second axes of flow are situated in a co-planar arrangement. Upward movement of the actuation member causes the first contact element to engage said first valve seat and isolate said first flow passage from fluid communication with the common flow passage. A downward movement of the actuation member causes said second contact element to engage said second valve seat and isolate said second flow passage from fluid communication with the common flow passage. The valve stem and first contact element may be comprised of the same material. Also, the material used for the stem and body portion may be of a fluoropolymer material.  
         [0010]     A feature and advantage of certain embodiments of the invention relative to typical diaphragm-type three-way valves is that the source passages and common passage are co-planar, allowing the valve to be utilized in situations where space is at a premium. The present invention has this feature while retaining the flexibility that pneumatic actuation provides.  
         [0011]     Yet another feature and advantage of specific embodiments of the invention relative to diaphragm-type valves is that there is no need for a diaphragm to control the valve thereby reducing the number of components, reducing assembly costs, and allowing the valve to occupy a smaller volume than current three-way valves.  
         [0012]     A feature and advantage of various embodiments of the present invention relative to existing stack valve designs is a three-dimensional control contour assembly that is snap-fit together, allowing the valve core to be assembled quickly and efficiently without need for press fit tooling. As a result, the valve is less expensive to manufacture than present three-way valves.  
         [0013]     Still yet another feature and advantage of specific embodiments of the invention is that the valve body may be molded rather than machined.  
         [0014]     Another feature and advantage of specific embodiments of the invention is that the three-dimensional control contour can be quickly and easily removed from the connecting passage for replacement.  
         [0015]     Further disclosure relating to plastic valves suitable for use in the semiconductor processing industry and for handling caustic fluids can be found in U.S. Pat. Nos. 5,335,696; 5,279,328; and U.S. application Ser. No. 08/843,456; now U.S. Pat. No. 5,924,441, all of which are assigned to the assignee of the instant invention. The two patents and the application are hereby incorporated by reference herein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a drawing of a prior art three-way valve;  
         [0017]      FIG. 2  is a perspective view of a three way valve according to the invention;  
         [0018]      FIG. 3  depicts a three-way valve according to an embodiment of the invention;  
         [0019]      FIG. 4  depicts a valve stem in an embodiment of the invention;  
         [0020]      FIG. 5  illustrates an embodiment of a three-way valve according to the invention;  
         [0021]      FIG. 6  illustrates a poppet as used in an embodiment of the present invention; and  
         [0022]      FIG. 7  depicts a poppet as used in an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]     It is noted that while the ensuing discussion describes various components as “upper” and “lower,” such descriptions are relational only; the embodiments disclosed do not require any particular orientation, nor do they require a certain portion of the valve be located above another portion.  
         [0024]     Referring to  FIGS. 2 and 3 , a configuration of a three-way stack valve  50  according to the present invention is presented in isometric projection in an upright orientation. The three-way stack valve  50  alternates the flow of fluid between a common passage  52  and either an upper passage  54  or a lower passage  56 . The passages  52 ,  54  and  56  may be formed within a valve body  58  and may also have threads  60  formed thereon for coupling with external piping (not depicted). A covering  61  may be used to shroud the upper workings (discussed below) of the stack valve  50 . The valve body  58  may be constructed of a fluoropolymer material through an injection molding and/or machining process.  
         [0025]     The upper passage  54  expands into an upper chamber  62  also formed within the valve body. Likewise, the lower passage  56  diverges into a lower chamber  64 . A connecting passage  66  generally centered about a central axis  68  establishes fluid communication between the upper and lower chambers  62  and  64 . The connecting passage  66  is also in fluid communication with the common passage  52 .  
         [0026]     An upper valve seat  70  aligned with central axis  68  is situated at the bottom  72  of the upper chamber  62 , thus forming a flow transition between the upper chamber  62  and the connecting passage  66 . Likewise, a lower valve seat  74  aligned with central axis  68  is formed at an upper end  76  of the lower chamber  64 , transitioning between the lower chamber  64  and the connecting passage  66 .  
         [0027]     The upper chamber  62  of the  FIG. 3  embodiment contains an upper valve assembly  78  having an upper poppet portion  80 , a flexible portion  82  and an upper cap portion  84 . The upper valve assembly  78  may also be made from a fluoropolymer material selected for resistance to the caustic process fluids. There are certain advantages to selecting a material that is resilient, as will be evidenced by the discussion below.  
         [0028]     The upper poppet portion  80  is aligned and configured to cooperate with the upper valve seat  70  to isolate the upper chamber  62  from the connecting passage  66  when the upper poppet portion  80  is seated against the upper valve seat  70 . An actuating rod or member  86  is connected to the upper poppet portion  80 , extending upward through the flexible portion  82  and through an access port  88  in the upper cap portion  84 . A threadable connection between the actuating member  86  and the upper poppet portion  80  is portrayed in  FIG. 3 ; however, any attachment means recognized by those skilled in the art may be utilized. The depiction of  FIG. 3  also portrays the upper poppet portion  80  as having a female receptacle  90  with a mouth  92  on a lower face  94  of the upper poppet portion  80 . The receptacle  90  is for receiving a lower valve assembly  96  (discussed below).  
         [0029]     Preferably, the various portions  80 ,  82  and  84  of the upper valve assembly  78  are integral with each other, either being formed from a single continguous material, or fused or glued or otherwise joined permanently together, to form an impervious barrier between the fluid stream  18  and interior of the upper valve assembly  78  that houses the actuating member  86 .  
         [0030]     The  FIG. 3  embodiment depicts the flexible portion  82  as having a bellows wall  98  that allows the upper poppet portion  80  to follow the actuating member  86  along central axis  68 . The bellows wall  98  provides a flexible barrier between the interior of the upper valve assembly  78  and the fluid stream  18 . As such, the bellowed wall  98  provides flexibility akin to a diaphragm, but within a smaller diameter or footprint. Other configurations for the flexible portion  82  may also be employed, such as an elastic sleeve, or a pair of concentric sleeves with a sliding seal therebetween, or other linearly extendible barriers known in the art.  
         [0031]     The upper valve assembly  78  is suspended within the upper chamber  62  by mounting the upper cap portion  84  to the valve body  58  at an upper end  100  of the upper chamber  62 . The upper cap portion  84  may be configured to seat within a radial groove  102  that cooperates with the upper chamber  62  to form a continuous lip  104  on the valve body  58  near the upper end  100  of the upper chamber  62 . The upper cap portion  84  is secured in place by a plug  106  that is seated in a recess  108  on an upper surface  110  of the valve body  58 . The plug  106  has an access port  112  aligned with the central axis  68  through which the actuating member  86  passes.  0 -rings or other seals  114  and  116  are disposed within the access port  112  and at the interface between the perimeter of the plug  106  and the recess  108  to contain any fluid that may leak between the upper cap portion  84  and the valve body  58 .  
         [0032]     The lower chamber  64  is bounded on a lower end  118  by a lower end cap  120 . The lower end cap  120  may be configured to seat within a radial groove  122  that, in conjunction with the lower chamber  64 , forms a continuous lip  124  near the lower end  118  of the lower chamber  64 . The lower end cap  120  is secured in place by a blind flange  126  connected to the valve body  58  (connection not depicted). An o-ring or other sealing means  128  is disposed between the blind flange  126  and the valve body  58  to contain any fluid that may leak between the lower end cap  120  and the valve body  58 .  
         [0033]     The lower valve assembly  96  includes a unitary stem  132  and a lower poppet portion  134 . By “unitary,” it is meant that the stem  132  is formed from a single solid material, with no covering sleeve, such that the outer surface of the stem is in wetted contact with the process fluid being controlled. An upper portion  136  of the unitary stem  132  is formed to mate with the receptacle  90  of the upper poppet portion  80 . The upper portion  136  of the unitary stem in the  FIG. 3  configuration is depicted as having a male frustum portion  138  and a detent portion  140 . If the upper poppet portion  136  is fabricated from a resilient material, the frustum portion  138  aids in the insertion of the lower valve assembly  96  into the female receptacle  90 . During assembly, the male frustum portion  138  causes the mouth  92  of the female receptacle  90  to expand momentarily as the upper portion  136  passes through the mouth  92 . Once the detent portion  140  passes through the mouth  92 , the mouth  92  of the receptacle  90  elastically constricts or “snaps back” into place, and the detent portion  140  engages with an interior portion about the periphery  142  of the mouth  92  to secure the lower valve assembly  96  in place.  
         [0034]     Accordingly, a “snap on,” “snap fit” or “snap together” assembly is hereby defined as one in which portions of a resilient female component elastically stretches or expands momentarily as a male component passes through or into the female component, the female component returning substantially to its original shape after the components are joined.  
         [0035]     Alternatively, the receptacle  92  and the upper portion  136  of the unitary stem  132  may be threadably engaged, as illustrated in  FIG. 4 . Such a configuration precludes the “snap fit” assembly of the  FIG. 3  embodiment, but is still conducive to hand assembly. A threadable engagement  130  is particularly suited for materials that lack resiliency.  
         [0036]     Preferably, the lower poppet portion  134  and the unitary valve stem  132  of  FIG. 3  are integrally formed, but they may be formed separately and joined by fusing, threading or by other joining means known in the art. The lower valve assembly  96  is aligned and configured to cooperate with the lower valve seat  74  to isolate the lower chamber  64  from the connecting passage  66  when the lower poppet portion  134  is seated against the lower valve seat  74 . Because the unitary valve stem  132  is formed from a single, corrosion resistant material, there is no need for the protective sleeve  16  depicted in  FIG. 1 ; hence, there is no leak path that can form through the unitary valve stem  132 .  
         [0037]     The method of assembling the configuration of  FIG. 3  is as follows: Provide a valve body  58  having formed therein an open upper chamber  62 , an open lower chamber  64 , a connecting passage  66  and a recess  108 . Also provide an upper valve assembly  78 , a lower valve assembly  96 , a lower end cap  120 , a blind flange  126 , a plug  106  and an actuating member  86 . Feed the actuating member  86  through the access port  88  of the upper cap portion  84  and the flexible portion  82  of the upper valve assembly  78 , and attach the actuating member to the upper poppet portion  80 . Place the upper valve assembly  78  into the upper chamber  62  and position the upper cap portion  84  so as to form a closure over the upper chamber  62 . Secure the upper valve assembly  78  in place by sliding the access port  112  of the plug  106  over the actuating member  86  and into the recess  108 , and fastening the plug  106  to the valve body  58 . Feed the lower valve assembly  96  through the open lower chamber  64  and the connecting passage  64  so that the upper portion  136  of the unitary stem  132  is aligned with the mouth  92  of the receptacle  90  located on the lower end of the upper poppet portion  80 . Exert a force against lower valve assembly  96  so that the frustum portion  138  of the upper portion  136  of the lower contact element  96  causes the mouth  92  of the receptacle  90  first to expand, then to snap back into place as the upper portion  136  of the unitary stem  132  passes through the mouth  92  of the receptacle  90 . Position the lower end cap  120  so as to form a closure with the lower chamber  64 . Secure lower end cap in place by connecting the blind flange  126  to the valve body  58 .  
         [0038]     Referring to  FIG. 5 , an alternative stack valve configuration  51  is depicted wherein a unitary stem  144  is integral to an upper valve assembly  146  instead of a lower poppet portion  148 . A receptacle  150  having a mouth  158  is formed within the lower poppet portion  148  and mates with the unitary stem  144  in the same manner as described for the  FIG. 3  embodiment. The mating between the unitary stem  144  and the lower poppet portion  148  depicted in  FIG. 5  has the same features as the corresponding mating parts in the  FIG. 3  embodiment—namely, an end portion  152  having a frustum portion  154  for ease of assembly and a detent portion  156  to secure the unitary stem within the receptacle  150 .  
         [0039]     The method for assembling the configuration of  FIG. 5  is as follows: Provide a valve body  58  having formed therein an open upper chamber  62 , an open lower chamber  64 , a connecting passage  66  and a recess  108 . Also provide an upper valve assembly  78 , a lower valve assembly  96 , a lower end cap  120 , a blind flange  126 , a plug  106  and an actuating member  86 . Feed the actuating member  86  through the access port  88  of the upper cap portion  84  and the flexible portion  82  of the upper valve assembly  78 , and attach the actuating member  86  to the upper poppet portion  80 . Place the upper valve assembly  78  into the upper chamber  62  with the unitary stem  144  substantially centered within the connecting passage  66 . Position the upper cap portion  84  so as to form a closure over the upper chamber  62 . Secure the upper valve assembly  78  in place by sliding the access port  112  of the plug  106  over the actuating member  86  and into the recess  108  and fastening the plug  106  to the valve body  58 . Through the open end of the lower chamber  64 , align the mouth of the receptacle  150  with the end portion  152  of the unitary stem  144 . Apply a force against lower poppet portion  148  so that the frustum portion  154  on the end portion  152  of the unitary stem  144  causes the mouth  158  of the the receptacle  150  first to expand, then to snap back into place as the end portion  152  of the unitary stem  144  passes through the mouth  158  of the receptacle  150 . Position the lower end cap  120  so as to form a closure with the lower chamber  64 . Secure lower end cap in place by connecting the blind flange  126  to the valve body  58 .  
         [0040]     Referring to  FIGS. 6 and 7 , the  FIG. 5  embodiment can be exploited for easy disassembly by implementing a few modifications. Specifically,  FIG. 6  depicts an end portion  152  of the unitary stem  144  having no detents. Instead, the detents are eliminated in favor of an inclined surface  160  that may have an angle substantially similar to the angle of the surface of the frustum portion  154  that transitions between the unitary stem  144  and the end portion  152  of the unitary stem  144 . When the lower chamber  64  is in an “open” position (i.e. is not seated against the lower valve seat  74 ), as depicted in  FIG. 6 , removal of the lower poppet  148  is augmented by the inclined surface  160 . The inclined surface  160  will cause the mouth  158  of the receptacle  150  to widen as the end portion  152  passes through the mouth, according to the same dynamic as the “snap on” of the poppet during assembly. However, when the lower poppet  148  is seated in the “closed“position (i.e. is seated against the lower valve seat  74 ) by a seating force  166  as depicted in  FIG. 7 , a reaction force  162  having a radial inward component  164  is exerted against the lower poppet  148  that prevents the inclined surface  160  from expanding the mouth  158  of the receptacle  150 ; hence, detents are not necessary to secure the lower poppet  148  in the  FIG. 6  embodiment.  
         [0041]     Accordingly, the lower poppet  148  in  FIG. 6  may be readily removed by grasping the lower poppet  148  when the lower chamber  64  is open to the connecting passage  66  and pulling the lower poppet  148  off the end portion  152  of the unitary stem  144 . Once lower poppet  148  has been removed, the stack valve assembly  50  may be readily disassembled by removing the lower blind flange  126  and the plug  106 .  
         [0042]     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive.