Abstract:
An actuator assembly for a slit valve door is configured to maintain a slit valve in a closed condition notwithstanding a high pressure differential between adjacent chambers that the slit valve isolates from each other. The slit valve door actuator assembly includes an actuator which moves the slit valve door between open and closed positions, and a locking mechanism to keep the slit valve door in a position to seal the slit valve in resistance to high gas pressure against the slit valve door. The locking mechanism may include a hard stop which is selectively movable into position to block retracting movement of the slit valve door.

Description:
FIELD OF THE INVENTION 
   This invention is generally concerned with processing systems used for processing substrates, and is more particularly concerned with actuating a slit valve door which seals a slit valve opening between two chambers in a vacuum processing system. 
   BACKGROUND OF THE INVENTION 
   Conventional techniques for manufacturing flat panel displays or semiconductor devices entail applying a sequence of processes to a substrate such as a glass plate or a silicon wafer. The processes to be applied may include thermal processing, physical vapor deposition (PVD), chemical vapor deposition (CVD), etching, etc. Typically, each process in the sequence of processes is performed in a respective processing chamber. Accordingly, the substrates upon which the processes are performed must be transferred from one processing chamber to another. 
   It is also conventional to incorporate a number of different processing chambers in a single processing tool, wherein the processing chambers are coupled along the periphery of a central transfer chamber.  FIG. 1  is a schematic side view of a conventional processing tool  11 . The processing tool  11  includes a centrally-positioned transfer chamber  13 . A load lock chamber  15  and a processing chamber  17  are shown coupled to respective sides of the transfer chamber  13 . One or more additional processing chambers and/or load lock chambers, which are not shown, may also be coupled to respective sides of the transfer chamber  13 . The load lock chamber  15  is provided to accommodate introduction of substrates into the processing tool  11  from outside the processing tool  11 . 
   The transfer chamber  13  includes a main body  19  having side walls  21  (of which only two are visible in  FIG. 1 ). Each side wall  21  may be adapted to have a load lock or processing chamber coupled thereto. The transfer chamber  13  also includes a top  23  supported on the main body  19 . A lid  25  is provided to sealingly close the top  23  of the transfer chamber  13 . 
   A lower end of the transfer chamber  13  is closed by a substantially annular bottom  27 . The bottom  27  of the transfer chamber  13  has a central aperture  29  which accommodates installation of a substrate handling robot  31  in the transfer chamber  13 . The substrate handling robot  31  is adapted to transfer substrates among the processing chambers  17  and the load lock chamber or chambers  15  coupled to the transfer chamber  13 . 
   To minimize the possibility of contamination of substrates processed in the processing tool  11 , it is customary to maintain a vacuum in the interior of the transfer chamber  13 . Hence, the processing tool  11  may be referred to as a vacuum processing system. A pumping system, which is not shown, may be coupled to the transfer chamber  13  to pump the transfer chamber  13  down to a suitable degree of vacuum. 
   Also illustrated in  FIG. 1  is an actuator  33  which selectively opens and closes a slit valve  35  associated with the processing chamber  17 . When the slit valve  35  is in an open position (not shown), a substrate may be introduced into or removed from the processing chamber  17 . When the slit valve  35  is in the closed position illustrated in  FIG. 1 , the processing chamber  17  is isolated from the transfer chamber  13  so that a fabrication process may be performed on a substrate within the processing chamber  17 . 
     FIG. 2  is a schematic vertical cross-sectional view showing on a larger scale the slit valve  35  and associated actuator  33  of the processing tool  11 . The slit valve  35  is adapted to selectively seal a passage  37  which, when the slit valve  35  is in an open condition (not shown) communicates between the transfer chamber  13  and the processing chamber  17 . The passage  37  terminates at a slit-shaped opening  39  on the processing chamber side of the passage  37 , and terminates in a slit-shaped opening  41  on the transfer chamber side of the passage  37 . 
   A door seating surface  43  surrounds the opening  41  and may be part of the sidewall  21  of the transfer chamber  13 . In accordance with a known practice, the door seating surface  43  defines a plane which is inclined at an angle (e.g., 45°) from a path (indicated by arrow  45 ) by which a substrate (not shown) is transferred through the passage  37 . A slit valve door  47  is mounted on a second end  49  of an actuator shaft  51  that is part of the actuator  33 . The slit valve door  47  is adapted to selectively seal against the seating surface  43  so as to gas-tightly isolate the processing chamber  17  from the transfer chamber  13 . In particular, the slit valve door  47  may include an O-ring (not separately shown) to form a seal between the slit valve door  47  and the door seating surface  43 . The sealing position of the slit valve door  47  is indicated in solid lines in  FIG. 2 . The actuator  33  is operable to retract the slit valve door  47  to a position shown in phantom and indicated as  53 . When the slit valve  47  is in its retracted position  53 , the slit valve  35  is in an open condition, and the passage  37  is not obstructed by the slit valve door  47 , so that a substrate may be transferred between the transfer chamber  13  and the processing chamber  17 . 
   The conventional slit valve arrangement may also include a bellows (not shown so as to simplify the drawing) which is connected between the second end  49  of the actuator shaft  51  and the bottom  27  of the transfer chamber  13 . The bellows may be provided to seal around the actuator shaft  51 . 
   As noted above, it is customary to maintain a vacuum pressure in the transfer chamber  13  during processing operations. A process which may be performed in the processing chamber  17 , such as chemical vapor deposition or etching, may call for maintaining a high pressure (e.g., 5 atmospheres) in the processing chamber  17  during processing. In order to maintain isolation between the transfer chamber  13  and the processing chamber  17  while a high pressure process is performed in the processing chamber  17 , it is necessary that the slit valve door  47  be held against the sealing surface  43  with a force sufficient to resist the force exerted in an outward direction (i.e., from the processing chamber  17  toward the transfer chamber  13 ) by the pressurized gas in the processing chamber  17 . 
   As the dimensions of the processing tool  11  are increased to accommodate processing of larger substrates, the size of the slit valve door  47  is increased, and of particular concern in the present instance, the surface area of the slit valve door  47  exposed to the passage  37  is increased. Consequently, the effective force applied by the pressurized gas in the processing chamber  17  against the slit valve door  47  is increased. The increase pressure experienced by the slit valve door  47  leads to a need to increase the force with which the slit valve door  47  is held against the door sealing surface  43 . To provide such an increased sealing force, it could be contemplated to increase the size of the actuator  33 . However, space considerations may make it impractical to increase the size of the actuator  33 . Furthermore, if the slit valve door  47  is pressed against the sealing surface  43  with the increased force (e.g., at a time when the processing chamber  17  is not pressurized), the O-ring which is intended to seal between the slit valve door  47  and the door sealing surface  43  may be compressed to such a degree that metal-to-metal contact may occur between the slit valve door  47  and the door sealing surface  43 . Such metal-to-metal contact may generate particles, which may adversely affect the devices processed within the processing tool  11 . 
   SUMMARY OF THE INVENTION 
   According to an aspect of the invention, a slit valve door is movable by an actuator between a position in which the slit valve door seals a slit valve opening and a position in which the slit valve door does not obstruct the opening. A locking mechanism is associated with the actuator to limit movement of the slit valve door away from the slit valve opening. The locking mechanism is sufficiently robust to hold the slit valve door in a sealing position relative to the slit valve opening, notwithstanding a force exerted against the slit valve door by a high gas pressure in a processing chamber coupled to the slit valve opening. 
   With the locking mechanism (e.g., a hard stop) provided in accordance with the invention, the slit valve door may be held in position against a door sealing surface in a manner so as to withstand the high pressure present within the processing chamber, without requiring a larger slit valve door actuator, and without requiring compression of a compressible member such as an O-ring to such a degree that metal-to-metal contact may occur between the slit valve door and the door sealing surface. 
   Further features and advantages of the present invention will become more fully apparent from the following detailed description of exemplary embodiments, the appended claims and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a vertical cross-sectional view of a conventional vacuum processing system in which the present invention may be applied; 
       FIG. 2  is a vertical cross-sectional view showing a conventional slit valve that selectively isolates two chambers of the vacuum processing system of  FIG. 1 ; 
       FIG. 3  is a perspective view of a slit valve door actuator assembly provided in accordance with the invention; 
       FIG. 4  is a perspective view of the inventive slit valve door actuator assembly of  FIG. 3 , in which the assembly has been rotated so that the path of travel of the slit valve door appears to be vertical, and the assembly is shown in a configuration in which the slit valve door is extended to seal a slit valve opening (which is not shown); 
       FIG. 5  is a view similar to  FIG. 4 , but showing the inventive slit valve door actuator assembly in a configuration in which the slit valve door is retracted so as not to obstruct a slit valve opening (which is not shown); 
       FIG. 6  is a perspective view of the inventive slit valve door actuator assembly of  FIG. 3  with a mounting bracket omitted and, with the assembly rotated such that the path of travel of the slit valve door appears to be vertical, and showing the inventive slit valve assembly positioned with the slit valve door extended so as to seal a slit valve opening (which is not shown); 
       FIG. 7  is a perspective view similar to that of  FIG. 6 , but showing the inventive slit valve door actuator assembly positioned with the slit valve door retracted so as not to obstruct a slit valve opening (which is not shown); 
       FIG. 8  is a schematic side view of the inventive slit valve door actuator assembly of  FIG. 3 , showing blocking and releasing positions of a hard stop relative to an actuator shaft; and 
       FIG. 9  is a flow chart that illustrates a method provided in accordance with the invention for operating a processing tool in which the inventive slit valve door actuator assembly is employed. 
   

   DETAILED DESCRIPTION 
   In accordance with the invention, an actuator for a slit valve door is equipped with a locking mechanism, to prevent the slit valve door from being pushed away from a slit valve opening by high pressures occurring in a processing chamber sealed by the slit valve door. By providing the locking mechanism, which may include a hard stop that interacts with a feature on the slit valve&#39;s actuator shaft, it is not necessary to provide an actuator that is large enough by itself to resist the high pressure generated in the processing chamber. 
   An embodiment of the invention will now be described with reference to  FIGS. 3–9 . 
     FIG. 3  is a perspective view of a slit valve door actuator assembly  101  provided in accordance with the invention.  FIGS. 4–7  are other perspective views of the inventive slit valve door actuator assembly  101 . The views presented in  FIGS. 4–7  are each rotated such that the path of travel of the slit valve door appears to be vertical, whereas, in a preferred embodiment of the invention, the path of travel of the slit door valve is inclined, as in the conventional slit valve arrangement shown in  FIGS. 1 and 2 . The inventive slit valve door actuator assembly  101  is shown in isolation in  FIGS. 3–7 , but in practice the inventive slit valve door actuator assembly  101  may be installed within a conventional processing tool, as depicted in  FIGS. 1 and 2  and as described in conjunction therewith.  FIGS. 4 and 6  show the inventive slit valve door assembly  101  in a position such that the slit valve door seals a slit valve opening (not shown);  FIGS. 5 and 7  show the inventive slit valve door assembly  101  in a position such that the slit valve door is retracted from a slit valve opening (not shown). In  FIGS. 6 and 7 , a mounting bracket  103  (see  FIGS. 3–5 ) of the inventive slit valve door actuator assembly  101  is omitted to simplify the drawing. 
   The inventive slit valve door actuator assembly  101  may include an actuator  105  (best seen in  FIGS. 6 and 7 ) such as a pneumatic actuator, a hydraulic actuator or the like. The actuator  105  may include an actuator housing  107  and an actuator shaft  109 . The actuator shaft  109  has a first end  111  (visible, e.g., in  FIGS. 5–7 ) and a second end  113 . A pneumatic or hydraulic cylinder or the like, may be coupled to the first end  111  of the actuator shaft  109 . 
   A slit valve door  117  is mounted on the second end  113  of the actuator shaft  109 . The slit valve door  117  includes a backing plate  119  and an elastic body  121  supported on the backing plate  119 . The elastic body  121  may be, for example, an O-ring. The slit valve door  117 , including the backing plate  119  and the elastic body  121 , may be configured in accordance with conventional practices to seal against a surface such as the surface  43  shown in  FIG. 2  when the slit valve door  117  is pressed against the surface by the actuator  105 . That is, the slit valve door  117  is configured to selectively sealingly close the opening  41  of the passage  37  between the transfer chamber  13  and the processing chamber  17  (see  FIG. 1 ). It will be appreciated that the slit valve door  117  may be considered to be a sealing member and/or the elastic body  121  may be considered to include a sealing surface. 
   The inventive slit valve door actuator assembly  101  further includes a locking mechanism  123 , which is adapted to selectively limit movement of the slit valve door  117  toward the actuator housing  107  by selectively limiting travel of the actuator shaft  109 . In one embodiment of the invention, the locking mechanism  123  may include a stop feature  125  on the actuator shaft  109  such as a washer, nut or other laterally extending feature, a slot or other similar feature formed within the actuator shaft  109 , or the like which may be positioned on the actuator shaft  109  at a location that is intermediate the slit valve door  117  and the actuator housing  107 . The locking mechanism  123  further comprises a hard stop  127  which is selectively positionable so as to interact with the stop feature  125 . Other stop features and/or stop feature and hard stop locations may be employed. For example, the stop feature could be positioned on the slit valve door (e.g., so as to extend from a backside thereof) and the hard stop positioned to selectively interact therewith. 
   In  FIGS. 3 ,  4  and  6 , the stop feature  125  has a circular profile and hence is disk shaped, although other shapes may be employed. A bore (not visible in the drawings) may be provided at a central portion of the stop feature  125  to receive the actuator shaft  109  therethrough. In one or more embodiments of the invention, the bore of the stop feature  125  may be threaded, or the stop feature  125  may be associated with one or more threaded features (e.g., nut  129  seen in  FIGS. 3 ,  4 ,  6 ), and an outer surface of the actuator shaft  109  may be provided with threading (not shown) so that the position of the stop feature  125  along the actuator shaft  109  can be adjusted. 
   The locking mechanism  123  further includes a hard stop actuator assembly  133 . The hard stop actuator assembly  133  is coupled to the hard stop  127  and is adapted to move the hard stop  127  between a blocking position, which is indicated in phantom as  135  in  FIG. 8  and a release position, which is indicated as  137  in  FIG. 8 . The blocking position  135  may also be referred to as a first hard stop position and the release position  137  may also be referred to as a second hard stop position. When the hard stop  127  is in the blocking position  135 , it obstructs a path of travel  139  ( FIG. 8 ) of the stop feature  125 . When the hard stop  127  is in the release position  137  it does not obstruct the path of travel  139  of the stop feature  125 . 
   The hard stop actuator assembly  133  includes an actuator  141  ( FIGS. 3–7 ) such as a pneumatic actuator, or the like. The hard stop  127  has a first side  155  ( FIG. 7 ) and a second side  157 . A slot  160  is formed in the second side  157  of the hard stop  127 . The slot  160  may be configured so that the hard stop  127  partially surrounds the actuator shaft  109  when the hard stop  127  is in the blocking position  135  (see  FIG. 8 ). Preferably, the hard stop  127  does not contact the actuator shaft  109  at any time, except for contacting the stop feature  125  as described below. 
   As indicated in  FIG. 7 , the inventive slit valve door actuator assembly  101  may include, or have associated therewith, a controller  171 . The controller  171  is operatively coupled to the actuators  105  and  141  so as to control operation thereof. The controller  171  may optionally be arranged to control aspects of a processing tool (e.g., processing tool  11  of  FIG. 1 ) in addition to the actuators  105 ,  141 . The controller  171  may be programmed to cause a processing tool to perform the process described below in connection with  FIG. 9 . 
   Operation in accordance with the inventive slit valve door actuator assembly  101  will now be described with reference to  FIG. 9 , and with further reference to  FIGS. 4–7 .  FIG. 9  is a flow chart that illustrates a process that may be performed by using a processing tool like that depicted in  FIGS. 1 and 2 , with the inventive slit valve door actuator assembly  101  of  FIGS. 3–8  installed therein. 
   Prior to the beginning of the process of  FIG. 9 , the slit valve door  117  is in a retracted position (as shown in  FIGS. 5 and 7 ) such that the slit valve door does not obstruct the opening of the slit valve (e.g., the opening  41  shown in  FIG. 2 ). Consequently, the processing chamber  17  is in communication with the transfer chamber  13  via the passage  37 . Also, both the transfer chamber  13  and the processing chamber  17  may be in an evacuated condition. 
   The process of  FIG. 9  begins with a step  201 , in which a substrate (not shown) to be processed in the processing chamber  17  is transferred into the processing chamber  17  from the transfer chamber  13  by the substrate handling robot  31 . The robot  31  then withdraws from the processing chamber  17  leaving the substrate in the processing chamber  17 , and step  203  follows. At step  203  the controller  171  ( FIG. 7 ) controls the actuator  105  to extend the actuator shaft  109  so that the slit valve door  117 , and in particular the elastic body  121 , is pressed against the door seating surface  43  ( FIG. 2 ). A seal is thereby formed around the opening  41 . With substantially equal pressure in both the processing chamber  17  and the transfer chamber  13  (e.g., with both chambers evacuated), the elastic body  121  is compressed to a degree such that the backing plate  119  and the actuator shaft  109  are in a first sealing position. The slit valve door  117  may also be considered to be in a first sealing position. 
   With the slit valve door  117  in the first sealing position, the stop feature  125  of the locking mechanism  123  is positioned as shown in  FIG. 8 , with a small clearance to allow the hard stop  127  to be moved from its release position  137  to its blocking position  135 . The amount of clearance may be, for example, on the order of several mils. It will be appreciated that the position of the stop feature  125  along the actuator shaft  109  may have been adjusted during installation of the slit valve door actuator assembly  101  to provide the desired clearance. 
   Step  205  follows step  203 . At step  205  the controller  171  controls the hard stop actuator  141  so that the hard stop  127  coupled thereto is moved from the release position  137  to the blocking position  135 . 
   A process, such as chemical vapor deposition, etching, etc., to be performed with respect to the substrate in the processing chamber  17  may now begin. A gas pressure required for that process is provided within the processing chamber  17 , as indicated by step  207 . As noted above, a high gas pressure (e.g., about five atmospheres, although other pressures may be employed) may be required. The resulting pressure differential between the processing chamber  17  and the transfer chamber  13  generates a large force that is applied to the slit valve door  117  in a direction opposite to the force applied by the actuator  105 . The force of the gas pressure from the processing chamber side may be sufficient to overcome the force of the actuator  105  so as to push the slit valve door  117  toward the actuator housing  107  by a small amount until the stop feature  125  contacts the hard stop  127 , which is in the blocking position  135 . The elastic body  121  remains compressed (although to a lesser degree than when the slit valve door  117  is in the first sealing position) and the slit valve opening  41  remains sealed by the slit valve door  117 . At this time, the actuator shaft  109  and the backing plate  119  (and hence the slit valve door  117 ) may be considered to be in a second sealing position, in which, for example, the actuator shaft  109  extends from the actuator housing  107  by a shorter distance than when the slit valve door  117  is in the first sealing position. 
   The process performed within the processing chamber  17  is completed as indicated at step  209  in  FIG. 9 . The processing chamber  117  is then evacuated, as indicated at step  211 . With evacuation of the processing chamber  117 , there may be substantially no pressure differential across the slit valve door  117 , and therefore no substantial force from gas pressure within the processing chamber  117  to oppose the force of the actuator  105 . Accordingly, the degree of compression of the elastic body  121  may be increased, and the slit valve door  117  is returned to the first sealing position. Accordingly, the stop feature  125  may return to a position such that it no longer contacts the hard stop  127  and the clearance between the stop feature  125  and the hard stop  127  is restored. 
   Following step  211  is step  213 . At step  213 , the controller  171  controls the actuator  141  to retract the hard stop  127  coupled thereto. As a result, the hard stop  127  is retracted and moved from its blocking position  135  to its release position  137 . Consequently, the hard stop  127  is no longer in the path of travel  139  ( FIG. 8 ) of the stop feature  125 . This allows the slit valve door  117  to be retracted from the door seating surface  43 , as indicated at step  215 . In particular, the controller  171  now controls the actuator  105  to retract the slit valve door  117 . As a result, the slit valve door  117  is placed in a position (e.g., the position indicated as  53  in  FIG. 2 ) so that the slit valve opening  41  and passage  37  are no longer obstructed thereby. The robot  31  then enters the processing chamber  17  to transfer the substrate from the processing chamber  17  to the transfer chamber  13 , as represented by step  217  in  FIG. 9 . The process of  FIG. 9  is then complete. Note that the force applied by the slit valve door actuator may be maintained throughout the process, or may be turned off after the hard stop locks the slit valve door in the closed position. 
   During the processing of large substrates (e.g., 300 mm), the size and geometry of the slit valve door  117 , and the pressure in the processing chamber  17  may be such that the force of the processing chamber gas pressure upon the slit valve door  117  becomes very large (e.g., about 1,500 lbs. or more against the actuator  105  if a large pressure differential exists across the slit valve door  117 , such as when a processing chamber gas pressure of about 5 ATM or more is employed). The stop feature  125  and the hard stop  127  are dimensioned, and are constructed of materials selected, such that the locking mechanism  123  is able to hold the slit valve door  117  at the second sealing position, not withstanding the large force applied to the slit valve door  117  by the gas pressure inside the processing chamber  17 . In one such embodiment, even though a force of about 1,500 lbs. or more may be applied against the actuator  105  (due to a large pressure within the processing chamber  17 ), the actuator  105  coupled to the slit valve door  117  has a bore diameter (B.D.) of about 2 inches, and only exerts a force necessary to obtain an adequate degree of compression of the elastic body  121  to place the slit valve door  117  in the first sealing position. By way of comparison, if the locking mechanism  123  were not provided, it might be necessary to provide a pneumatic actuator having a B.D. of greater than 5 inches to produce a force sufficient to maintain the slit valve door  117  in place against the gas pressure inside the processing chamber  17 . The actuator  105  may comprise, for example, a conventional pneumatic or other similar actuator. The hard stop actuator  141  may have, for example, about a one inch B.D., and also may be a conventional actuator. Other bore diameters may be employed. As an alternative to a pneumatic actuator, other types of actuators may be employed, including, for example, a hydraulic actuator or a motor driven arrangement (e.g., a lead screw or other connecting structure that couples the motor to the hard stop  127 ). 
   Instead of employing a conventional O-ring as the elastic body  121 , other arrangements may be provided, including a molded-in-place seal such as that disclosed in U.S. Pat. No. 6,089,543, which is incorporated herein in its entirety by this reference. The backing plate  119  may comprise one or more members, and may assume other shapes for supporting the elastic body  121 . The stop feature  125  and the hard stop  127  may have other configurations than those illustrated herein. 
   The feature on the actuator shaft  109  with which the hard stop  127  interacts need not extend outwardly from the shaft diameter. For example, the feature may be a notch, a step, or a circumferential channel adapted to be engaged by the hard stop. 
   The foregoing description discloses only exemplary embodiments of the invention; modifications of the above disclosed apparatus which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For example, the transfer chamber in which the inventive slit valve door actuator assembly may be installed may have a domed bottom, as disclosed in U.S. Provisional Patent Application Ser. Nos. 60/390,629 and 60/392,578 rather than the generally flat transfer chamber bottom illustrated in  FIG. 2  hereof. The above-referenced commonly-owned provisional patent applications are hereby incorporated by reference herein in their entirety. 
   Although the inventive locking mechanism  123  illustrated above is associated with a central portion of the actuator shaft  109  of the slit valve door actuator  105 , other locking mechanism arrangements may be provided in accordance with the invention. For example, an alternative locking mechanism may include one or more stop members that extend within the actuator housing  107  and that selectively prevent the pressure disk  115  from moving in the direction away from the seating surface  43  when the slit valve door  117  is pressed against the seating surface  43 . Other alternative embodiments of the locking mechanism may also be provided. 
   Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.