Abstract:
A pendulum gate valve including an expandable gate which pivots when unexpanded to selectively block a vacuum or other pressure-differential passage. The valve includes a valve plate sealing one side of the passage and a ring abutting an opposed side of the passage when the gate member is expanded. A compression spring biases apart the valve plate and ring to close the valve by means of respective two-stage hangers attached thereto, extending along the spring, and having distal ends capturing the spring. Pneumatic pressure applied to a pneumatic cavity formed between the middles of the two-stage hangers and accommodating the spring forces apart the valve plate and ring to open the valve in the blocking position. Thereby if pressure fails, the valve fails to a sealed state. The axially movable valve plate is advantageously water cooled to allow use with a heated processing chamber.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a pendulum or slider valves having a gate laterally movable into and out of a passageway sealable by the gate. In particular, the invention relates to such valves having gates which move laterally into the passageway in a compressed condition and can expand axially to seal the passageway. 
       BACKGROUND ART 
       [0002]    Many types of processing equipment include a processing chamber operating at reduced pressure or in controlled ambient but require a sealable passageway into the processing chamber to allow a workpiece being processed or a large equipment used in the processing to be transferred between the processing chamber and the exterior or another chamber at least occasionally at a different pressure or ambient. As a result, the passageway needs be open for passage of the substrate or insertion of the equipment but closed during other phases of operation. That is, a large valve is required. Two additional requirements for the valve maybe the high temperatures required within the adjacent processing chamber and that the action of the valve creates very few particles which would contaminate the processing chamber. 
         [0003]    Two related valve types are often used if the passageway needs to be not only large but approximately circular. In a first type called a pendulum gate valve or swing valve, also simply referred to as a pendulum valve, a gate capable of sealing the passageway rotates about an axis offset from the passageway from a retracted position away from the passageway to an active or blocking position in the passageway at which it blocks the passage or large articles through the passageway. In a second type called a slider or shuttle valve, the gate moves laterally along a generally linear axis between the retracted and blocking positions. In either case, once the gate has reached the blocking position, it may block the passageway but it does not necessarily form a vacuum seal. To complete the sealing of the passageway, the gate needs to move generally along the axis of the passageway to engage a sealing surface surrounding the passageway. When the passageway needs to be unblocked, the gate needs to move away from the sealing surface before it is moved out of the passageway. 
         [0004]    Although the invention is not so limited, one application of such valves involves the Czochralski growth of silicon ingots or boules in which a crucible filled or recharged with chunks or pellets of silicon is heated to above the melting point of silicon, approximately 1416° C., so that a melt of liquid silicon exists in the crucible. A small seed of silicon is lowered to the surface of the melt. If monocrystalline silicon is desired, the silicon seed should be monocrystalline and of the desired crystalline orientation. By careful control of temperatures near the silicon melting point, the liquid silicon freezes on the silicon seed and the seed grows into a larger piece of silicon of the same crystalline orientation as that of the seed. The growing silicon piece is slowly withdrawn and the process continues so that the width and axial length of the piece continues to increase. Again by careful control of temperatures and other growth parameters, the lateral size can be restrained to a desired diameter, for example, 200 mm or 300 mm desired for the present generation of silicon wafers. The desired product is a generally cylindrical ingot of monocrystalline silicon of the desired diameter and perhaps 2 m long. As the lower end of the ingot grows, the ingot is slowly drawn upwards into a pull chamber above the crucible. After the desired length of ingot is grown, the ingot is tapered down, separated from the melt, and withdrawn into the pull chamber. At least during the melting and growth of the silicon ingot, the crucible chamber should be maintained in an inactive ambient, for example, of argon, and preferably at a reduced pressure typically in the range of 10 to 50 Torr. 
         [0005]    In batch Czochralski growth, the crucible is loaded with silicon chunks sufficient to complete the growth of one ingot. After the one ingot is grown, the crucible is typically cooled and then discarded and a new crucible is used for the next ingot. In batch Czochralski, it is typical to selectively isolate the pull chamber from the crucible chamber during the long heat up of the crucible and its charge and then to quickly lower the seed crystal from the pull chamber. Also, it is desirable to cool the ingot independently of the crucible. Conventionally, the valve between the crucible and pull chambers has been implemented as a flapper valve, which is effective but occupies valuable height in the pull chamber. It is desired to make the pull chamber as long as possible without requiring an excessively high ceiling in the factory. 
         [0006]    In recharge Czochralski, after the growth of one ingot, the crucible is recharged with another batch of silicon chunks and the process is repeated for additional ingot. However, the recharge should be performed without significantly cooling the crucible and without disturbing the desired ambient of the crucible chamber. As a result, the new charge of silicon should be introduced through a load lock involving some kind of valved passageway. 
         [0007]    In continuous Czochralski, only a limited amount of silicon is melted in the crucible but solid silicon is continuously or at least intermittently added to the crucible during the Czochralski drawing process and is immediately melted to augment the liquid. Additionally, multiple ingots are sequentially grown while the crucible remains filled with substantially the same amount of silicon melt. Clearly, the pull chamber must be valved to allow removal of the last grown ingot and the insertion of a new seed. Also, it is desired that the solid silicon charge contained in a hopper be pressurized to pressure of the crucible chamber be less than the total charge required for the lifetime of the crucible. Therefore, some valving is required to isolate the crucible chamber from the hopper when it is being recharged even if this occurs during removal of a grown ingot. In a variant of continuous Czochralski, the silicon is pre-melted outside the crucible and flowed into the crucible to maintain a constant melt level in the crucible, but valving is still required to recharge the pre-melter with additional solid silicon. 
         [0008]    Valves used in these Czochralski processes are subject to the two additional requirements of high temperature and low particulate production. Valves facing the interior of the crucible chamber operate with the gate facing a very hot crucible or crucible furnace but seals such as elastomeric O-rings fail well below the temperature of the melted silicon. Secondly, valves need to generate a minimum of particles which could fall into the crucible and contaminate the silicon ingot being produced. However, most valves involve some sort of sliding motion between two adjacent parts typically composed of stainless steel or other contaminating material. 
         [0009]    Many pendulum valves accomplish the axial sealing motion by providing an axial movement to the shaft providing the rotary motion to the gate. However, axial movement of the rotary shaft is considered to generate excessive bending on the rotary shaft and large-area gate to provide the large sealing forces required to seal the gate and also to produce undesired particulates by the mechanical movements next to the passageway. 
         [0010]    A valve should also be fail safe, for example, during a power failure or pump failure, and not uncontrollably change from its sealed to an unsealed condition or vice versa. 
       SUMMARY OF THE INVENTION 
       [0011]    A pendulum or shuttle gate valve in which an axially expandable gate while in its compressed state is movable transversely to a vacuum-sealable passageway between a retracted position away from the passageway and a blocking position in the passageway. While in the blocking position, the gate can be expanded in both axial directions to both vacuum seal the passage and to forcibly abut an opposed surface to counteract the sealing force. 
         [0012]    A pendulum valve rotates the gate about an axis offset from the passageway. A shuttle valve linearly moves the gate perpendicularly to an ax is of the vacuum passageway. 
         [0013]    Compression springs are supported to axially bias the valve plate and ring in opposed outward directions to close the valve. Positive pneumatic pressure can force the valve plate and ring in opposed inward directions to unseal the valve while the gate is in the blocking position. 
         [0014]    The valve plate may be cooled by water or other liquid supplied through flexible tubing connecting the axially movable valve plate and liquid passages in the arm moving the pendulum valve gate between its retracted and blocking positions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an orthographic view of an embodiment of a pendulum gate valve of the invention. 
           [0016]      FIG. 2  is an orthographic partially sectioned view of the pendulum gate valve of  FIG. 1  taken along another direction. 
           [0017]      FIG. 3  is an orthographic view of the gate of the pendulum gate valves of  FIGS. 1 and 2 . 
           [0018]      FIG. 4  is a plan view of the gate of  FIG. 3 . 
           [0019]      FIG. 5  is a sectioned side view of the pendulum gate valve of  FIGS. 1 and 2  including the gate of  FIGS. 3 and 4 . 
           [0020]      FIG. 6  is a sectioned side view of the gate of  FIGS. 3 and 4  in its expanded state taken along section line B-B of  FIG. 4 . 
           [0021]      FIG. 7  is a sectioned side view of the gate of  FIG. 6  in its compressed state taken along the same section line. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    One embodiment of a pendulum valve  10  of the invention, illustrated in the unsectioned orthographic view of  FIG. 1  and a sectioned orthographic view of  FIG. 2 , includes a gate  12  illustrated in the blocking position adjacent a tapped flange  14  attached to an inner side of a two-piece vacuum-tight valve housing  16 . Another tapped flange  18 , shown in  FIG. 2 , is attached to the outer side of the valve housing  16 . The flanges  14 ,  18  may be fixed by bolts and vacuum sealed to respective chambers selectively maintained at different pressures or ambients. The circular bores of the two flanges  14 ,  18  may be used to define a vacuum port with a passageway extending along a central passage axis  20  and which is selectively sealed by the gate. The inner side may be exposed to a hot environment, such as the previously described Czochralski furnace. Nearly all internal parts of the valve  10  except flexible seals may be constructed of stainless steel. 
         [0023]    The gate  12 , also illustrated in the orthographic view of  FIG. 3  and the plan view of  FIG. 4 , is supported through a radially extending support arm  22  on a rotary shaft  24  extending along a pivot axis  26  aligned parallel to but offset from the passage axis  20  of the vacuum port and thereby pivots about the pivot axis  26 . Returning to  FIG. 2 , the rotary shaft  24  is fixed externally of the valve housing  16  to a lever arm  28  which extends away from the pivot axis  26  and is connected to an actuator  30  through a double-pivoting link  32  to allow the actuator  26  to move the gate  12  between the illustrated blocking position adjacent the flanges  14 ,  18  with the lever arm  24  engaging a stop  34  on the housing  16  and an open, retracted or storage position  36 , generally indicated by dotted line  36  in  FIG. 2 . That is, the gate  12  supported by support arm  22  on the rotary shaft  24  is rotated by the actuator  30  between the retracted position  36  and the blocking position in the passageway illustrated in  FIG. 2 . In the retracted position  36 , the gate  12  remains within the valve housing  16  but leaves clear the vacuum port for passage of fairly large items the size of the inner diameters of the flanges  14 ,  18 . The retracted position  36  generally underlies the unpatterned portion of the top of the valve housing  16  and under the joint between the two portions of the valve housing  16 . The actuator  30  needs to move the gate  12  between only two positions so that a solenoid linear actuator maybe used, but pneumatic actuators, motor-drive worm drives, geared drives, or other types of actuators may be substituted. Many of the already described parts are conventional and are commercially available, for example, from GNB Corporation of Elk Grove, Calif. 
         [0024]    The internals of the pendulum valve  10  and its gate  12  are illustrated in more detail in the side cross-sectional view of  FIG. 5  taken along section line A-A of the plan view of  FIG. 4 . Bearings  36  rotatably support with minimal axial movement the rotary shaft  24  in a first mounting plate  38  sealed to the outer side of the valve housing  16 . A first rotary seal  40  in a second mounting plate  42  and a second rotary seal  44  in a third mounting plate  46  sealed to the inner side of the valve housing  16  provide a vacuum seal to the rotary shaft  24  between the exterior and interior of the valve housing  16 . 
         [0025]    The rotary shaft  24  is fixed to the radially extending arm  22  and is integral or, in the illustrated embodiment, fixed to a generally annular middle plate  50  arranged about a gate axis  52 , which is generally coincident with the vacuum passage axis  20  when the gate  12  is in the illustrated blocking position. The middle plate  50  includes a handle  54  extending radially outwardly, which is fixed to the support arm  22  and thus to the rotary shaft  24 . 
         [0026]    The gate  12  is illustrated in  FIG. 5  in its blocking but unsealed or contracted position. It includes on its inner (lower as illustrated) side a valve plate  56  with an annular O-ring groove  58  which seals to a sealing surface at the backside of the inner flange  18  when the gate  12  is axially expanded. A folded spiral cooling channel  60  is formed in the valve plate  56  and is sealed by a generally circular cooling cover  62 . 
         [0027]    The gate  12  is further illustrated in its compressed state in the cross-sectional view of  FIG. 6  and in its expanded state in the cross-sectional view of  FIG. 7 , both taken along the bent section line B-B of  FIG. 4 . Three or more (four in the illustrated embodiment) segmented inner risers  64 , also called plate links and illustrated in the plan view of  FIG. 4 , are arranged around the periphery of the cooling cover  62  and attached valve plate  56 . The inner risers  64  connect, as best shown in  FIGS. 6 and 7 , the cooling cover  62  and attached valve plate  58  to an outer plate  66 , also called a carrier, located on the other, outer (upwards as illustrated) side of the gate  12 . The outer plate  66  has an outer flat-surface flange  68  on its exterior side and an inwardly extending annular rim  70  on its inner side. A circular cap seal  74 , which is generally planar with the outer surface of the rim  68 , is fixed and vacuum sealed by an O-ring to the outer plate  66  to vacuum seal a central aperture in the outer plate  66 . The central aperture forms part of the pneumatic chamber to be described later. 
         [0028]    The gate  12  further includes on its inner side a generally circular inner plate  84  attached through three or more (four as illustrated) segmented outer risers  86  to an outer annular abutment ring  88  on the other side of the gate  12 . As shown in  FIG. 5 , the outer riser  86 A adjacent the support arm  22  includes a slot  90  to allow the handle  54  of the middle plate  50  to pass through with sufficient axial clearance to accommodate the expansion and compression of the gate  12 . The outer riser  86 B opposite the support arm  22  similarly includes a lower aperture to accommodate with sufficient axial clearance a generally vertically ascending cooling stem  92  to be fixed to the cooling cover  62  to provide cooling water or other type of chilling liquid to the cooling channels of the valve plate  58 . The inner plate  84  is not fixed to the valve plate  58  and a gap between them varies as the gate  12  expands and contracts. Similarly, although the abutment ring  88  and the outer plate  66  are approximately of the same height, they are not fixed together and a relative axial displacement between them varies as the gate  12  expands and contracts. 
         [0029]    As shown in  FIGS. 3 and 4 , the outer risers  86  are interleaved with the inner risers  64  in a generally circular arrangement about the gate axis  52 . In the expanded state of the gate  12  illustrated in  FIG. 6 , the abutment ring  88  engages an annular abutting surface  94  of the interior side of the outer flange  14  of  FIG. 5 . In this embodiment, no O-ring is provided at the interior surface of the outer flange  14  and the engagement between the outer flange  14  and the abutment ring  88  chiefly provides an equal and opposite counter-force to the sealing force against the inner flange  18  to thereby reduce or eliminate any torquing or bending of the rotary shaft  24  and support  22  and to allow for sealing forces greater than what the support arm  22  itself could provide. That is, the sealing force is not transmitted through the support arm  22  and the rotary shaft  30  but is exerted generally axially between the flanges  14 ,  18  and the intermediate abutment ring  88  and valve plate  56 . Either or both of the abutment ring  88  and the abutting surface  94  need not be continuous and may be segmented. 
         [0030]    The inner plate  84  also includes a center post  100 , to which is fixed an inverted annular spring cap  102 , for example, by threads between the post  100  and cap  102 . The spring cap  102  has an annular rim  104  extending radially outward from the interior side of the post  100 . 
         [0031]    A compression spring  106  is compressed between the rim  104  of the spring cap  102  connected to the inner plate  56  and the rim  70  of the outer plate  66 . The spring cap  102  and middle portions of the outer plate  66  act as respective hangers extending from the inner plate  56  and the outer portions of the outer plate across the space occupied by the spring  106 . When the spring  106  is in compression, it presses apart the two rims  70 ,  104  but inversely pulls apart the abutment ring  88  and the valve plate  56 . That is, the spring  106  biases the gate  12  to its expanded or sealed condition. The spring  106  may be formed of Belleville washers, which are conically shaped washers of spring material. When multiple Belleville washers are stacked with alternating conical slopes, they act as a strong compression spring. The spring  106  and associated spring holder  102  maybe assembled through the central aperture in the outer plate  66  opened by removing the spring cover or cap seal  74  and screwing the spring holder  102  onto the post  100  to thereby compress the spring  106 . 
         [0032]    A first annular bellows  110  provides an axially expandable vacuum seal and wall between the middle plate  50  and the outer plate  66  and a second annular bellows  112  similarly provides an axially expandable vacuum seal and wall between the middle plate  50  and the inner plate  84 . Thereby, an expandable pneumatic chamber  114  is formed inside the bellows  110 ,  112 , the outer plate  66 , and the inner plate  84  including a vertical passage  115  through the middle plate  50  illustrated in  FIG. 5 . The compression spring  106  is disposed in and axially expands and contracts within the pneumatic chamber  114   
         [0033]    A selectable source of high pressure air or other gas is connected to the pneumatic chamber  114  through an axial bore  116  in the rotary shaft  24  and a radial bore  118  in the arm  50  and thence through a connected bore in the handle  54  to the vertical passage  115 . Positive gas pressure acts against the spring  106  to force apart the inner and outer plates  66 ,  84  and hence to move the abutment ring  88  and valve plate  56  in opposite directions toward the stationary middle plate  50 . That is, positive gas pressure axially compresses the gate  12  to its compressed state and opens the valve  10  although the gate  12  may remain in the blocking position in the vacuum port. On the other hand, at reduced pressure, for example, atmospheric pressure from the air source, the spring  116  forces apart the two rims  70 ,  114  and thus inversely forces apart the valve plate  56  and the abutment ring  88  to the compressed or unsealed state of the gate  12 . It is noted that the mechanical actuation components producing the expansion and compression of the gate  12  are contained within the pneumatic chamber  114  and are isolated from the perhaps hostile process environment and do not contribute contaminants to the process. 
         [0034]    The movement between the expanded and compressed states of the gate  12  maybe relatively small, for example, 0.110 inch (2.8 mm). Also, as evident from  FIG. 5 , the axial movement distances of the valve plate  56  and the abutment ring  88  maybe different. 
         [0035]    It is possible to design a simpler expandable gate in which the spring biases the gate to its closed position and relying upon negative gas pressure to open the valve. However, such a design is limited to a differential pressure of atmospheric pressure and may be inadequate to seal the gate when its outer side is at a lower pressure than its inner side. 
         [0036]    The pendulum valve of this embodiment has three normal states, a retracted state in which the gate is positioned away from the vacuum port, a blocking but unsealed state in which the gate is positioned in the vacuum port but is not expanded so that it does not seal, and a sealed state in which the gate is positioned in the vacuum port and is expanded so as to seal the vacuum port. The first state corresponds to a fully open condition of the valve; the third state to a fully closed condition. Normally, the gate is compressed in the retracted position and during movement between the retracted and blocking positions. 
         [0037]    In the case of power outage or loss of pneumatic pressure, a fully closed valve remains fully closed and an opened valve with the gate  12  in the retracted or storage position  36  remains open although the gate  36  will expand at the storage position  36  of the gate  12 . Further, if the processing chamber loses vacuum while the outer side of the valve remains at low pressure, the spring force can be of sufficient magnitude to maintain the seal in spite of the reverse pressure differential. That is, the valve  10  can seal in both directions of atmosphere to vacuum and vacuum to atmosphere. 
         [0038]    Cooling water or other cooling liquid is circulated through the cooling channel  60  formed in the valve plate  56  delivered into and from the valve  10  from flexible hoses through two axial cooling bores  120  formed in the rotary shaft  24  and unillustrated channels in the support arm  22 . However, the sealing plate  56  is axially movable over a small distance while the rotary shaft  24  is substantially fixed in the axial direction. As illustrated in  FIGS. 2 ,  3 , and  4 , flexible metal tubing of, for example, stainless steel form a supply tube  112  and a return tube  114 , which are welded or otherwise fixed on two respective ends to the respective channels formed in the support arm  22  and connected to the two cooling bores  120  at the inside of the valve housing  16  and on the other two respective ends to two water ports  126  (see  FIG. 5 ) formed in the cooling stem  92  located opposite the arm  22 . Both tubes  122 ,  124  extend circularly along peripheral paths outside the gate  12  and form respective near semi-circles. The two waters ports  126  in turn are connected through channels in the cooling stem  92  through the cooling cover  62  to opposite ends of the folded spiral cooling channel  60  formed in the valve plate  56 . The two ends of the cooling channel  60  are closely adjacent under the cooling stem  92  and the fold of the cooling channel  60  is near the center of the valve plate  56 , thereby cooling the valve plate  56  sufficiently to allow the use of fairly conventional O-rings placed in the valve plate O-ring grooves  58  to complete the sealing. The limited axial motion of the valve plate  56  relative to the axially fixed rotary shaft  24  is accommodated by the inherent flexibility of long thin-walled tubes  122 ,  124 . 
         [0039]    The valve of the invention can be advantageously used in a Czochralski growth system. In all types of Czochralski systems, a large valve of the invention with a vertical passageway may be interposed between the crucible chamber and the pull chamber to allow the two to be isolated before growth commences or to remove a grown boule and replace it with a new seed in both recharge and continuous Czochralski. Thereby, the pull chamber maybe made taller for a given ceiling height. A somewhat smaller valve of the invention with a generally horizontal passageway may be placed on the side of the crucible chamber to allow a feedstock injector to be introduced into the crucible chamber from a vacuum-pumped feed hopper to replenish silicon source material into the crucible. For recharge Czochralski, the injector maybe inserted only between growth cycles to completely fill the crucible for another boule. For continuous Czochralski, the injector remains within the chamber during a growth cycle, but it may need to be removed, without breaking the crucible chamber vacuum, to replenish the hopper or to perform emergency maintenance on the feed system without destroying the crucible. 
         [0040]    However, the valve of the invention is not limited to Czochralski growth systems and may be used in other applications. Further, although the above description emphasizes the reduced pressures or vacuum of the two chambers connected by the valve  10 , the valve  10  may be applied to systems in which one or both of the chambers is subjected to significant positive pressures. In this case, the strength of the spring  106  and the pressure of the pneumatic source may need to be increased to seal against the positive pressure in front of the valve plate  56 . 
         [0041]    It is appreciated that the expandable gate can be easily adapted for use in a shuttle valve in which an expandable gate moves linearly in a direction transverse to the passageway between a retracted position and a blocking position and is expanded in place. That is, the arm  50  is reconfigured to linearly move the gate  10  into and out of the passage way. Sliders and tracks can be advantageously used. 
         [0042]    It is also appreciated that the valve passageway and associated gate and flanges need not be circular but may assume other shapes to accommodate the cross-section of objects being passed through the valve. 
         [0043]    The invention thus allows a high-temperature, minimally contaminating gate valve to be formed with few modifications from commercially available valves. Further, the gate valve may be made fail-safe against power, pneumatic, and pump failures.