Patent Application
20110006235
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
One embodiment of a pendulum valve 10 of the invention, illustrated in the unsectioned orthographic view of
The gate 12, also illustrated in the orthographic view of
The internals of the pendulum valve 10 and its gate 12 are illustrated in more detail in the side cross-sectional view of
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.
The gate 12 is illustrated in
The gate 12 is further illustrated in its compressed state in the cross-sectional view of
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
As shown in
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.
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.
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
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.
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
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.
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.
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.
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
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.
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.
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.
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.
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.
