Abstract:
A non-contaminating gas-tight valve for controlling a flow of granular polysilicon. The valve has a spherical valve member formed from single-crystal polysilicon, so that any particles worn from the valve member during use will be non-contaminating polysilicon. The valve member has a passage through which granular polysilicon flows when the valve is in an open position. When rotated perpendicular to the flow, the passage no longer permits movement of granular polysilicon through the valve. The valve member has a smooth finish and is wiped clean when rotated against non-abrasive upper and lower seats, reducing the likelihood of valve member wear. A cavity between the valve member and the valve body allows for removal of excess granular polysilicon from the valve, inhibiting the valve from seizing due to excess granular polysilicon slipping past the upper valve seat and accumulating within the valve. The valve additionally forms a gas-tight seal between an upstream and downstream side of the valve.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to valves and more particularly to a non-contaminating and gas-tight valve designed for regulating a flow of granular polysilicon through the valve. 
     Conventionally, valves of various construction regulate flows of liquid, solid, and semi-solid materials. Common valve types include globe valves, gate valves, check valves, butterfly valves, and ball valves. Each valve type is specifically suited to a particular application. Adjustable ball valves are conventionally used in applications where the valve adjusts between fully open and fully closed. Although not specifically designed to throttle flow, ball valves may be adjusted between open and closed positions to throttle or adjust flow. Ball valves typically contain a metallic, plastic, or ceramic ball, which is rotatable about an axis perpendicular to the flow. A cylindrical channel passes through the center of the ball. When the channel is perpendicular to the flow, the valve is closed. When the channel is parallel to the flow, the valve is open. When the ball is at any point in between, the valve is partially open. 
     Depending upon the material and environmental requirements, valves are typically constructed of plastic, metal, rubber, and ceramic parts. As with all mechanical apparatus with moving parts, valves are susceptible to wear. Moving parts rubbing against one another and matter flowing through the valve contacting the parts causes valve wear. Dust and particle accumulation on a valve&#39;s moving parts also causes wear during operation. Wear inevitably leads to contamination of the material flowing through the valve by particles generated from the valve wear. Such wear may or may not be acceptable depending upon the purity requirements of the material flowing through the valve. In the semiconductor industry, handling of granular polysilicon requires minimal particulate contamination. As such, conventional valves having metallic or plastic parts have substantial drawbacks when applied to granular polysilicon because foreign particulate matter from the valve as it wears will inevitably contaminate the granular polysilicon. Therefore, there is a need for a valve which (1) is wear resistant and (2) is less apt to cause contamination as a result of wear. 
     SUMMARY OF THE INVENTION 
     Among the several objects of this invention may be noted the provision of such a valve that avoids generation of metallic particles or other contaminants without compromising sealing integrity; the provision of such a valve that is wear resistant; the provision of such a valve that inhibits the valve from seizing due to excess material accumulating within the valve; the provision of such a valve that has non-contaminating members holding the moving parts of the valve in place; and the provision of such a valve that forms a gas-tight seal between an upstream and downstream side of the valve through a single gas-tight seat placed between the moving valve member and the valve body. 
     In general, a valve apparatus for controlling a flow of granular polysilicon is disclosed. The valve apparatus inhibits contamination of the granular polysilicon by foreign materials. The valve apparatus comprises a valve body having an inlet and an outlet sized and shaped to allow granular polysilicon to flow into and out of the valve body. The valve apparatus additionally comprises a movable valve member arranged within the valve body for regulating the flow through the valve body. The movable valve member is formed from single-crystal silicon to reduce valve wear and inhibit creation of metal particles or similar contaminants within the flow of granular polysilicon. The movable valve member is movable between an open position where the granular polysilicon may flow through the valve body and a closed position where the granular polysilicon cannot flow through the valve body. 
     In a second embodiment of the present invention, a valve member formed from single-crystal silicon generally as set forth above is disclosed. 
     In a final embodiment of the present invention, a granular polysilicon handling system for controlling a flow of granular polysilicon is disclosed. The handling system comprises at least one material hopper sized and shaped to hold granular polysilicon within the system and at least one valve apparatus as set forth above. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a granular polysilicon handling system having at least one non-contaminating gas-tight valve; 
     FIG. 2 is a vertical section of the non-contaminating gas-tight valve of the present invention; 
     FIG. 3 is a vertical section of an upper body of the valve; 
     FIG. 4 is a vertical section of a lower body of the valve; 
     FIG. 5 is a vertical section of an upper body insert of the valve; 
     FIG. 6 is a bottom plan view of the upper body insert of FIG. 5; 
     FIG. 7 is a vertical section of an upper annular seat of the valve; 
     FIG. 7A is an enlarged, partial vertical section of the upper annular seat of FIG. 7; 
     FIG. 8 is a bottom plan view of the upper annular seat of FIG. 7; 
     FIG. 9 is a front elevation of a valve member of the valve; 
     FIG. 10 is a right side elevation of the valve member of FIG. 9; 
     FIG. 11 is a top plan view of the valve member; 
     FIG. 12 is right side elevation of an actuation chord of the valve member of FIG. 11; 
     FIG. 13 is a front elevation of a valve stem of the valve; 
     FIG. 14 is a left elevation of the valve stem of FIG. 13; 
     FIG. 15 is a vertical section of a carrier of the valve; 
     FIG. 16 is a top section of the carrier of FIG. 15; 
     FIG. 17 is a left elevation of the carrier of FIG. 15; 
     FIG. 18 is a vertical section of a lower annular seat of the valve; 
     FIG. 19 is a top plan view of the lower annular seat of FIG. 18; 
     FIG. 20 is a vertical section of a lower body insert of the valve; and 
     FIG. 21 is a bottom plan view of the lower body insert of FIG.  20 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and specifically to FIG. 1, a granular polysilicon handling system is generally indicated at  31 . The manufacture of granular polysilicon requires frequent product handling in a vertical direction. Handling systems are typically comprised of a series of valves and pipes connecting multiple pieces of material handling equipment, including hoppers, portable vessels, and reactors. FIG. 1 shows a schematic of such a system  31 . The schematic shows only the substantive components of the system  31 , removing several piping connections for simplicity. The granular polysilicon enters the system  31  through an inlet hopper  33  located at the top of the system. It then passes from the inlet hopper  33  through a non-contaminating gas-tight valve  41  of the present invention (FIG.  1 ). The non-contaminating gas-tight valve  41  will be described in detail below. In the overall handling system  31 , the valve  41  can isolate portions of the handling system so that granular polysilicon and gas cannot pass through the valve. Below the gas-tight valve  41 , the granular polysilicon enters a vessel  43  for treatment of the granular polysilicon. The treated polysilicon then passes through another gas-tight valve  41 , finally entering an outlet hopper  47  (FIG.  1 ). 
     Referring now to FIG. 2, a non-contaminating gas-tight valve of the present invention  41  is shown. The valve generally comprises an upper body  51  having an inlet  53  (FIG. 3) and a lower body  55  having an outlet  57  (FIG.  4 ). The upper body  51  has a lower annular flange  61 , and the lower body  55  has an upper annular flange  63 . The upper body  51  mounts on the lower body  55  such that the lower annular flange  61  abuts the upper annular flange  63 . An elastic sealing element  64 , such as an o-ring, fits between the upper and lower flanges  61 , 63 , forming a seal between the upper and lower bodies  51 , 55  (FIG.  2 ). The lower flange  61  contains a plurality of unthreaded bolt holes  65  while the upper flange  63  contains a plurality of threaded holes  67 . When the upper body  51  mounts on the lower body  55 , the unthreaded holes  65  match positions with the threaded holes  67  so that threaded studs  73  may be inserted downwardly through the upper body  51  and threaded into the lower body  55 . Nuts  74  thread down over the threaded studs  73  and bear against the upper body  51 , holding the valve  41  together (FIG.  2 ). In the preferred embodiment, multiple threaded studs  73  and nuts  74  secure the upper and lower bodies  51 , 55  together. Additionally, the upper body  51  and lower body  55  of the preferred embodiment are preferably formed from metal, such as stainless steel. Other materials exhibiting adequate strength and rigidity characteristics may also be used without departing from the scope of the invention. 
     The valve  41  is designed to control a flow of granular polysilicon within the handling system  31  and create a gas-tight seal within the system. The granular polysilicon is fed through the valve  41  by gravity. When the valve  41  is closed, no granular polysilicon flows through the valve. When the valve  41  is open, granular polysilicon will flow downward through the valve, entering the valve at the top of the upper body  51  and exiting the valve at the bottom of the lower body  55 . 
     Upon entering the valve  41 , the granular polysilicon passes through an upper body insert  75  (FIGS. 2,  5 , and  6 ). The upper body insert  75  is annularly shaped, fitting snugly within the mating cylindrical inlet  53  formed in the upper body  51  of the valve  41 . The upper body insert  75  has a passage  77  formed vertically through the insert (FIG.  5 ). The passage  77  is the first passage the granular polysilicon flows through as it travels through the valve  41 . The upper edge of the cylindrical passage is defined by a chamfer  79 . The upper body insert  75  should be constructed of a material that can direct large quantities of granular polysilicon into the valve  41  while minimizing the number of foreign particles contaminating the system due to wear of the insert. In the preferred embodiment, the upper body insert  75  is formed from single-crystal silicon so that any wear of the insert within the flow of granular polysilicon will only minimally contaminate the system  31 , since the particles created are single-crystal silicon of purity equivalent to that of granular polysilicon. 
     After flowing through the upper body insert  75 , the granular polysilicon passes through an upper annular seat  85 , as shown in FIGS. 2,  7 , and  8 . The upper annular seat  85  is generally ring-shaped. The seat  85  is received against an annular shoulder  87  formed in the upper body  51 . The seat  85  additionally has a frustoconical inlet face  89 , which is wider than the cylindrical passage  77  of the upper insert  75 , such that the granular polysilicon will flow from the upper insert through an opening  90  in the annular seat with little contact with the annular seat (FIG.  2 ). The seat  85  has a frustoconical outlet face  91  having two circumferential grooves  93  formed in its face (FIGS.  7  and  8 ). The grooves  93  create a series of three circumferential ridges  95 . In addition, the innermost ridge  95  has a lip  97 , which extends laterally inwardly from the seat  85 , as discussed infra (FIG.  7 A). 
     Below the upper annular seat  85  is the ball valve member  101  of the present invention, described in more detail below (FIGS. 2,  7 A,  9 - 11 ). The primary function of the upper annular seat  85  is to form a seal between the ball valve member  101  and the upper body  51 . In the preferred embodiment, the ball valve member  101  is a rotatable ball valve. The three circumferential ridges  95  of the annular seat  85  press against the ball valve member  101 , creating a tight seal between the valve and seat (FIG.  2 ). In the preferred embodiment, the annular seat  85  is formed from polytetrafluoroethylene so that the ball valve member  101  can move freely against the annular seat, while creating an adequate seal. 
     Referring now to FIGS. 9-11, the ball valve member  101  has a cylindrical passage  103  through the valve, allowing the flow of granular polysilicon to pass through the valve (FIG.  11 ). In an open position (as shown in FIG.  2 ), the passage  103  is oriented vertically so that the granular polysilicon can pass through the ball valve member  101 . The ball valve member  101  is rotatable about a horizontal axis A (FIG.  2 ), which is perpendicular to the cylindrical passage  103 . When the ball valve member  101  rotates ninety degrees, the solid portion of the valve member entirely covers the opening  90  in the upper annular seat  85 , blocking the flow of granular polysilicon or gas through the valve  41 . 
     As the ball valve member  101  rotates, the lip  97  wipes the surface of the valve member clean. The grooves  93  of the seat  85  allow for deformation of the outlet face  91 , so that the ridges can slightly deform during installation, conforming to the shape of the ball valve member  101 . When the ball valve member  101  rotates, excess granular polysilicon trapped between the valve member and ridges  95  can work into the grooves  93 , keeping the seal intact. The lip  97  presses firmly against the ball valve member, acting as a wiping element. In the preferred embodiment, the ball valve member  101  is manufactured from single-crystal silicon having a highly polished, mirror-like surface. Single-crystal silicon is rigid enough to create a tight seal with the upper annular seat  85 . More importantly, the wiping action, working jointly with the mirror-like surface of the ball valve member  101 , inhibits wear by reducing the tendency of the granular polysilicon to stick to the valve member, which can increase wear on the seat  85  by rubbing against the seat as the valve member moves. Any minimal wear of the ball valve member  101  will create single-crystal silicon particulate matter, which can be tolerated as a contaminant since the flow is granular polysilicon. Accordingly, creating a ball valve member  101  of single-crystal silicon reduces the likelihood of harmful contaminants within the flow of granular polysilicon material. Although single-crystal silicon is the preferred material for the valve member, it is envisioned that other materials such as silicon carbide, tungsten carbide, and silicon nitride may also be used without departing from the scope of the invention. 
     Because the ball valve member  101  must rotate within the body  51 ,  55 , a valve rotation mechanism is required to move the valve member within the valve  41 . Referring to FIGS. 9 and 10, a section of the ball valve member  101  is not completely spherical, but rather has a first flat face  109  on one side of the valve member. An actuation chord  111 , having a second flat face  113 , fits against the first face  109  of the ball valve member  101 , completing the spherical shape of the valve member (FIG.  11 ). The first and second flat faces  109 ,  113  each have four holes  115  in registration with each other (FIGS.  9 - 12 ). Four connecting pins  117  fit within the holes  115  of each face  109 ,  113  thereby connecting the two faces together in a fixed orientation. The actuation chord  111  and connecting pins  117  are preferably formed from stainless steel. Furthermore, a layer of adhesive material between the first face  109  and second face  113  holds the ball valve member  101  and actuation chord  111  together. In the preferred embodiment, the adhesive is an epoxy suitable for securing the ball valve member  101  valve to the actuation chord  111 . Finally, the actuation chord  111  has a rectangular notch  123  formed in its curved face, as further described below. 
     A ball valve stem  127  extends laterally from a side of the valve  41  for rotating the ball valve member  101  (FIGS. 2,  13 , and  14 ). The valve stem  127  is generally cylindrical in shape and designed to rotate along a central longitudinal axis A. The valve stem  127  passes through a cylindrical opening  129  formed within the lower body  55  (FIGS.  2  and  4 ). The valve stem  127  rotates freely on a bearing  130  within the opening  129  and is sealed in the lower body  55  by a seal  131  and seal compression nut  133  (FIG.  2 ). An inner end of the valve stem  127  has a key  135 . The key  135  engages the rectangular notch  123  formed in the actuation chord  111 . As the valve stem  127  rotates about its longitudinal axis A, the key  135  presses against the notch  123 , causing the entire ball valve member  101  to rotate with the valve stem. By rotating the valve stem  127 , a user can control valve position and flow through the valve. 
     Between the valve stem  127  and the actuation chord  111 , a carrier  141  acts to carry a shield  149  (FIGS. 2,  15 - 17 ). The carrier  141  is generally conical in shape, having an arcuate interior wall  143  which mates with the chord  111 . The carrier  141  inhibits granular polysilicon from contaminating the interface between the key  135  and the actuation chord  111 , where it could increase wear. Further, the exterior wall  145  of the carrier  141  is generally flat and includes an annular recess  147  formed about the edge to carry the shield  149 . The shield  149  fits between the carrier  141  and the upper and lower body  51 ,  55 , within the annular recess  147 , to protect the stem assembly from dust and other particulate matter (FIG.  2 ). In the preferred embodiment, the carrier  141  and shield  149  are formed from polytetrafluoroethylene, although other materials exhibiting similar characteristics are also contemplated as within the scope of the present invention. 
     Downstream of the ball valve member  101 , the granular polysilicon passes through a lower annular seat  155  (FIGS. 2,  18 , and  19 ). Like the upper annular seat  85 , the lower seat  155  is generally ring-shaped and presses against the ball valve member  101 . The seat  155  has a lower face  157  which rests against a shoulder  159  formed in the lower body  55 . The seat  155  has a frustoconical inlet face  161  having one circumferential groove  163  formed in its face (FIG.  18 ). This groove  163  is flanked by a pair of circumferential ridges  165  that extend from the frustoconical inlet face  161 . The circumferential ridges  165  of the lower annular seat  155  rest against the ball valve member  101 . 
     The gas-tight valve can accommodate granular polysilicon that may slip past the seal between the upper annular seat  85  and the ball valve member  101 . An annular cavity  171  formed between the body  51 , 55  and the ball valve member  101  allows the granular polysilicon to pass through the valve  41  should some slip past the seat  85 . The excess granular polysilicon then passes by gravity to the lower portion of the cavity  171 . To that end, the lower annular seat  155  has a plurality of drain holes  173  formed therein. The drain holes  173  connect the cavity  171  to the central portion of the valve  41 . These drain holes  173  allow excess granular polysilicon to exit the cavity  171 . Without these drain holes  173 , as with some previous valve designs, excess material can build up within the valve cavity  171 , causing the valve  41  to seize, wear, or fail. 
     Finally, the granular polysilicon passes through a lower body insert  177  (FIGS. 2,  20 , and  21 ). The lower body insert  177  is annular, fitting snugly within a mating cylindrical cavity formed in the lower body  55  of the valve  41 . The lower body insert  177  has a cylindrical passage  179  formed vertically through the insert. The cylindrical passage  179  is the last passage the granular polysilicon flows through as it travels through the valve  41 . The upper portion of the cylindrical passage  179  is defined by conical wall  181 , allowing the upper opening to be wider than the opening in the annular seat  155  or the ball valve member  101 . In the preferred embodiment, the lower body insert  177  is formed from single-crystal silicon so any insert wear creates particles within the flow of granular polysilicon that will not contaminate the system  31  because they are single-crystal silicon fragments. 
     The valve  41  of the preferred embodiment is operable over a pressure range of between about full vacuum to about 517 kilo-Pascals (75 pounds per square inch). The use of stainless steel, polytetrafluoroethylene, and single-crystal silicon for valve parts allows the valve to function within the given pressure range. In addition, the valve parts are designed to allow adequate part clearance when they expand or contract due to environmental or process conditions. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a,” “and “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.