Patent Publication Number: US-2012042828-A1

Title: Slit valve for vacuum chamber module

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of vacuum chamber modules, and more particularly to an improved slit valve used with such modules. 
     BACKGROUND OF THE INVENTION 
     Production of thin film photovoltaic (PV) modules (also referred to as “solar panels”) typically involves conveyance of a substrate, such as a glass panel, into and out of a vapor deposition chamber wherein a thin film layer of a semiconductor material is deposited onto the surface of the substrate. The process typically involves conveying the substrates through valves into and out of one or more vacuum chamber modules. The valves create a lock through which the substrates are conveyed and generally define a slot that is slightly larger than the cross section of the substrate in the open position of the valve. As such, the valves are generally referred to as “slit valves” in the art. 
     Conventional slit valves are typically a self-contained unit that includes a housing that mounts onto the vacuum chamber module. These valves are not versatile and can be quite expensive. Different valve configurations are needed for inlet valves and outlet valves. In addition, precise tolerances are needed for mating the valve housings onto the module housing to ensure proper operation of the valve and integrity of the vacuum chamber module during a vacuum process. Repair or replacement of the conventional slit valves can result in significant down time of the module, or the significant expense of maintaining an on-hand inventory of replacement valves. 
     Accordingly, the industry would benefit from an improved slit valve design particularly suited for vacuum chamber modules that is simple, robust, and eliminates certain of the disadvantages of conventional slit valves. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In accordance with aspects of the invention, a slit valve assembly is configured for attachment to any manner of vacuum chamber module, for example a module used in a vapor deposition processing line for the manufacture of solar panels. The valve assembly is provided to seal a slot opening in a wall of the module in a closed position, and to provide access through the slot opening in an open position for passage of substrates through the module. The valve assembly includes a rotatable shaft driven by a rotary actuator between an open rotational position and a closed rotational position. An elongated seal plate is configured with the shaft and has a sealing face configured for sealing against the module wall over the slot opening in the closed rotational position of the shaft. At least one arm member operably connects the seal plate to the shaft. A plurality of spaced apart arm members may be used for this purpose. The arm member is fixed to the shaft so as to rotate with the shaft and move the seal plate between the open and closed rotational positions. The arm member is pivotally attached to the seal plate and the seal plate is biased (i.e., by a spring or other biasing element) to an articulated position relative to the arm member. In this manner, as the shaft rotates towards the closed rotational position, an end of the seal plate initially engages the module wall and the seal plate pivots into a parallel sealing position relative to the module wall as the shaft continues to rotate to the closed rotational position. 
     In a particular embodiment, a compressible seal is provided on the sealing face of the seal plate, such as an O-ring seated with a groove defined in the sealing face. 
     In still another embodiment, a plurality of bearing supports may be configured along the rotatable shaft for mounting the shaft on the module wall. If the valve assembly is configured as an internal slit valve such that the seal plate is disposed within the module and seals against an internal face of the module wall, the bearing supports may have a standoff component so as to extend through bores in the module wall to mount to an external face of the module wall. If the valve assembly is configured as an external slit valve such that the seal plate seals against an external face of the module wall, the bearing supports may be mountable to the external face of the module wall. 
     Variations and modifications to the embodiments of the slit valve assembly discussed above are within the scope and spirit of the invention and may be further described herein. 
     The invention also encompasses any manner of vacuum chamber module for processing substrates in a vacuum. The module includes a housing having end walls with slots defined therein for passage of substrates into and out of the housing. A slit valve assembly in accordance with any of the embodiments described herein is configured on at least one of the end walls. In a unique embodiment, a slit valve assembly is provided at the inlet and outlet end walls of the module. 
     Variations and modifications to the embodiment of the vapor chamber module discussed above are within the scope and spirit of the invention and may be further described herein. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, is set forth in the specification, which makes reference to the appended drawings, in which: 
         FIG. 1  is front view of an exemplary vapor deposition system incorporating valve assemblies in accordance with aspects of the invention; 
         FIG. 2  is a perspective view of an embodiment of a slit valve assembly; 
         FIG. 3  is a side cut-away view of components of the valve assembly of  FIG. 2 ; 
         FIG. 4  is a perspective view of a module incorporating an inlet and an outlet slit valve assembly; 
         FIG. 5  is a perspective view of an interior portion of a module; and, 
         FIGS. 6 through 8  are sequential operational views of an embodiment of a slit valve assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention encompass such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  illustrates an embodiment of a vapor deposition system  10  that may incorporate various embodiments of a slit valve assembly  100  in accordance with aspects of the invention, particularly as components of various types of modules that make up the system  10 . For reference and an understanding of a particular environment in which the present slit valve assemblies  100  may be used, the system  10  of  FIG. 1  is described below, followed by a detailed description of particular embodiments of the slit valve assemblies  100 . It should be appreciated, however, that the slit valve assembly  100  is not limited to use in the system  10  of  FIG. 1 . Valve assemblies  100  may be used in any machine or system wherein vacuum slit valves are applicable. 
     The system  10  is configured for deposition of a thin film layer on a photovoltaic (PV) module substrate  14  (referred to hereafter as “substrate”). The thin film may be, for example, a film layer of cadmium telluride (CdTe). As mentioned, it is generally recognized in the art that a “thin” film layer on a PV module substrate is generally less than about 10 microns (um). Referring to  FIG. 1 , the exemplary system  10  includes a vacuum chamber  12  defined by a plurality of interconnected modules. Any combination of vacuum pumps  40  may be configured with the interconnected modules to draw and maintain a vacuum effective for the deposition process within the chamber  12 . A plurality of interconnected heater modules  16  define a pre-heat section of the vacuum chamber  12  through which the substrates  14  are conveyed and heated to a desired temperature before being conveyed into a vapor deposition apparatus  60 . Each of the modules  16  may include a plurality of independently controlled heaters  18 , with the heaters defining a plurality of different heat zones. A particular heat zone may include more than one heater  18 . 
     The vapor deposition apparatus  60  may take on various configurations and operating principles within the scope and spirit of the invention, and is generally configured for vapor deposition of a sublimated source material, such as CdTe, as a thin film on the PV module substrates  14 . In the embodiment of the system  10  illustrated in  FIG. 1 , the apparatus  60  is a module that includes a casing in which the internal components are contained, including a vacuum deposition head mounted above a conveyor assembly. 
     The vacuum chamber  12  also includes a plurality of interconnected cool-down modules  20  within the vacuum chamber  12  downstream of the vapor deposition apparatus  60 . The cool-down modules  20  define a cool-down section within the vacuum chamber  12  in which the substrates  14  having the thin film of sublimed source material deposited thereon are allowed to cool at a controlled cool-down rate prior to the substrates  14  being removed from the system  10 . Each of the modules  20  may include a forced cooling system wherein a cooling medium, such as chilled water, refrigerant, or other medium is pumped through cooling coils configured with the modules  20 . 
     In the illustrated embodiment of system  10 , at least one post-heat module  22  is located immediately downstream of the vapor deposition apparatus  60  and before the cool-down modules  20 . As the leading section of a substrate  14  is conveyed out of the vapor deposition apparatus  60 , it moves into the post-heat module  22 , which maintains the temperature of the substrate  14  at essentially the same temperature as the remaining portion of the substrate  14  within the vapor deposition apparatus  60 . In this way, the leading section of the substrate  14  is not allowed to cool while the trailing section of the substrate  14  is still within the vapor deposition apparatus  60 . If the leading section of a substrate  14  were allowed to cool as it exited the apparatus  60 , a non-uniform temperature would be generated longitudinally along the substrate  14 . This condition could result in the substrate breaking from thermal stress. 
     As diagrammatically illustrated in  FIG. 1 , a feed device  24  is configured with the vapor deposition apparatus  60  to supply source material, such as granular CdTe. Preferably, the feed device  24  is configured so as to supply the source material without interrupting the continuous vapor deposition process within the apparatus  60  or conveyance of the substrates  14  through the apparatus  60 . 
     Still referring to  FIG. 1 , the individual substrates  14  are initially placed onto a load conveyor  26 , and are subsequently moved into an entry vacuum lock station that includes a load module  28  and a buffer module  30 . A “rough” (i.e., initial) vacuum pump  32  is configured with the load module  28  to drawn an initial vacuum, and a “fine” (i.e., high) vacuum pump  38  is configured with the buffer module  30  to increase the vacuum in the buffer module  30  to essentially the vacuum within the vacuum chamber  12 . Slit valves  100  in accordance with aspects of the invention are operably disposed between the load conveyor  26  and the load module  28 , between the load module  28  and the buffer module  30 , and between the buffer module  30  and the vacuum chamber  12 . As described in greater detail below, these valves  100  are sequentially actuated by a motor or other type of actuating mechanism  102  in order to introduce the substrates  14  into the vacuum chamber  12  in a step-wise manner without affecting the vacuum within the chamber  12 . 
     An exit vacuum lock station is configured downstream of the last cool-down module  20 , and operates essentially in reverse of the entry vacuum lock station described above. For example, the exit vacuum lock station may include an exit buffer module  42  and a downstream exit lock module  44 . Sequentially operated slide valves  34  are disposed between the buffer module  42  and the last one of the cool-down modules  20 , between the buffer module  42  and the exit lock module  44 , and between the exit lock module  44  and an exit conveyor  46 . A fine vacuum pump  38  is configured with the exit buffer module  42 , and a rough vacuum pump  32  is configured with the exit lock module  44 . The pumps  32 ,  38  and slit valves  100  are sequentially operated to move the substrates  14  out of the vacuum chamber  12  in a step-wise fashion without loss of vacuum condition within the vacuum chamber  12 . 
     The system  10  also includes a conveyor system configured to move the substrates  14  into, through, and out of the vacuum chamber  12 . In the illustrated embodiment, this conveyor system includes the load conveyor  26 , exit conveyor  46 , and a plurality of individually controlled conveyor assemblies  56 , with each of the various modules including one of the conveyor assemblies  56 . Any combination of these conveyors,  26 ,  46 , and  56  may be configured in accordance with aspects of the invention, and the conveyors may include individual conveyor drive units  58  that control the conveyance rate of substrates  14  through the respective module. 
     As described, each of the various modules and respective conveyors in the system  10  are independently controlled to perform a particular function. For such control, each of the individual modules may have an associated independent controller  50  configured therewith to control the individual functions of the respective module, including the conveyance rate of the various conveyors and operation of the slit valves  100 . The plurality of controllers  50  may, in turn, be in communication with a central system controller  52 , as illustrated in  FIG. 1 . The central system controller  52  can monitor and control (via the independent controllers  50 ) the functions of any one of the modules so as to achieve an overall desired heat-up rate, deposition rate, cool-down rate, and so forth, in processing of the substrates  14  through the system  10 . 
     Referring to  FIG. 1 , the various modules may include active-sensing viewport assemblies  54  that detect the presence of the substrates  14  as they are conveyed through the module. The viewport assemblies  54  are in communication with the respective module controller  50 , which is in turn in communication with the central controller  52 . In this manner, the individual respective conveyor assemblies may be controlled to ensure that a proper spacing between the substrates  14  is maintained and that the substrates  14  are conveyed at the desired constant conveyance rate through the vacuum chamber  12 . It should be appreciated that the viewport assemblies may be used for any other control function related to the individual modules or overall system  10 . 
       FIG. 2  is a perspective view of an embodiment of a slit valve assembly  100 . The assembly  100  is particularly configured to be attached to a vacuum chamber module, such as any one of the modules  16 ,  20 ,  22 ,  42 ,  44 , and the like, of  FIG. 1 , as discussed above. It should be readily appreciated that the slit valve assembly  100  is not limited by its configuration with any particular type of module. 
     Referring to the sequential operational views of  FIGS. 6 through 8 , the slit valve assembly  100  is configured to seal a slot opening  106  in a wall  104  of any manner of vacuum chamber module in a closed position of the valve assembly  100  as illustrated in  FIG. 8 , and to provide access through the slot opening  106  in an open position of the valve assembly  100 . As discussed above with respect to  FIG. 1 , each of the slit valve assemblies  100  includes an actuating mechanism  102  ( FIG. 2 ) that moves the valve assembly  100  between the opened and closed positions. 
     Referring to  FIG. 2  in addition to  FIGS. 6 through 8 , the slit valve assembly includes a rotatable shaft  108  that is driven by the actuating mechanism  102 . In a particular embodiment, the actuating mechanism  102  may be any manner of conventional rotary actuator  110 . This actuator  110  may be, for example, an air drive actuator, piston-type drive actuator, vane-type drive, and the like. Rotary actuators are particularly useful in that they provide more than sufficient torque for the application and take up a relatively small operating area. It should be appreciated, however, that the actuating mechanism need not be a rotary actuator, but may be any type of drive for imparting rotational torque to the shaft  108 . 
     An elongated seal plate  112  includes a sealing face  114  that is configured to seal directly against the module wall  104  over the slot opening  106  in a closed rotational position of the shaft  108 , as depicted in  FIG. 8 . The seal plate  112  is operably connected to the shaft  108 , for example by at least one arm member  118 . In the illustrated embodiment, the seal plate  112  is connected to the shaft  108  by a plurality of spaced apart members  118 . It should be readily appreciated that any configuration of arm members  118  or other type of rigid or fixed connection between the seal plate  112  and shaft  108  may be utilized in this regard. 
     The arm members  118  are rotationally fixed to the shaft  108  so as to rotate with the shaft. At the same time, the arm members  118  are pivotally attached to the seal plate  112 , as particularly illustrated in  FIGS. 6 through 8 . The seal plate  112  is biased by a spring  126  or any other suitable biasing mechanism to an articulated non-parallel position relative to the arm member  118 , as depicted in  FIG. 6 . As the shaft  108  rotates towards its closed rotational position, an end  116  of the seal plate  112  is positioned so as to initially contact the face  138  (e.g., an internal face in the depicted embodiment) of the module  104 , as particularly depicted in  FIG. 7 . As the shaft  108  continues to rotate to the closed position, the seal plate  112  continues to pivot relative to the arm member  118  to a final sealing position wherein the seal plate  112  is parallel to and sealed against the module wall  104 . The seal plate may also be parallel to the arm member  118  in its sealed position, as depicted in  FIG. 8 . It should be understood that the degree of articulation between the seal plate  112  and arm members  118  is grossly exaggerated in  FIGS. 6 through 8  for purposes of explaining certain operational principles of the components. Depending on the system configuration, less than five degrees, or even less than two degrees, of articulation may be all that is necessary. 
       FIG. 3  is a more detailed cross-sectional view through certain components of the slit valve assembly  100  in its closed rotational position. In this particular embodiment, the slit valve assembly  100  is configured as an internal slit valve that is disposed within the vacuum chamber and thus rotates or swings between the opened and closed positions within the vacuum chamber. Referring to  FIG. 4 , an internal slit valve assembly  100  is illustrated on the right-hand side of the vertical vacuum chamber module  65  and an external slit valve assembly  100  is depicted on the left-hand side of the module  65 . The external slit valve assembly  100  seals against the outer external face  134  of the left-hand module wall  104  and, thus, swings between the opened and closed position externally of the vacuum chamber. 
     Referring to  FIGS. 2 and 3  in particular, any manner of suitable articulation joint  124  is configured between the arm members  118  and the seal plate  112 . In the illustrated embodiment, each of the arm members  118  is pivotally attached to the seal plate  112  by way of pivot blocks  125  that may be disposed on opposite sides of the arm members  118 . A pivot pin, axle, or like device extends through the pivot blocks  125  and the arm members  118  at the articulation joint  124 . A sufficient clearance is provided between the opposed surfaces of the arm members  118  and seal plate  112  to provide for the desired degree of articulation between the components. 
     Referring to  FIG. 3 , in a particular embodiment, a compressible seal may be provided on the seal face  114  of the seal plate  112 . For example, a compressible O-ring  120  may be seated within a groove  122  defined in the seal face  114 . The O-ring  120  compresses against the internal face  138  (or external face  134 ) as the seal plate  112  moves into its closed rotational position and, thus, ensures a vacuum seal over the slot opening  106 . Because of the biased articulation motion of the seal plate  112  relative to the shaft  108  and arm members  118 , once the seal plate  112  contacts the module wall  104 , the seal plate  112  is brought into a parallel, sealing configuration without causing rolling of the O-ring within the groove  122 . This is a significant advantage in that it substantially extends the life of the O-ring seal and also ensures a uniform application of sealing pressure around the slot opening  106 . 
     As particularly seen in  FIGS. 2 and 4 , a plurality of bearing supports  128  may be operationally disposed along the length of the shaft  108  for mounting onto the module wall  104 . The bearing supports  128  provide for the rotational movement of the shaft  108  and are rigidly fixed to the arm member  118  by any suitable means. The arm members  118  may be an integral component with the bearing supports  128 , or may be a separate component that is subsequently fixed to the bearing supports  128 . Referring to  FIGS. 3 and 5  wherein the slit valve assembly  100  is configured as an internal slit valve, the bearing support  128  may include a stand off component  132  (e.g., an extension) that extends through a bore  130  defined through the module wall  104 . In this manner, the bearing supports  128  can be affixed to the outer external face of the module wall  104 , for example by means of a flange  129  and bolts  131  instead of being mounted to the internal face  138 . This configuration provides significant advantages in maintenance and replacement of the slit valve components. Also, the external machined face of the module wall  104  is a precise reference surface datum for proper location of the bearing supports  128  (via the stand off components  132 ) relative to the inside face of the wall  104  to ensure proper orientation, movement, and sealing of the seal plate  112 . 
     In the embodiment wherein the slit valve assembly  100  is externally mounted, as in the left-hand embodiment in  FIG. 4 , the bearing supports  128  are mounted directly against the external face  134  of the module wall  104 . Because the shaft  108  does not penetrate through the module into the vacuum chamber, any manner of suitable bearing block  136  may be configured between the rotary actuator  110  and the external face  134  of the module wall  104 . However, when the slit valve assembly  100  is configured as an internal valve, as in the right-hand embodiment of  FIG. 4 , the shaft  108  penetrates through the side wall of the vacuum module  65 . Referring to  FIG. 5 , a shaft rotary seal  140  is provided for this purpose. The shaft rotary seal  140  may be any manner of rotary seal that is suitable for maintaining a vacuum seal around the shaft  108  at the location where the shaft penetrates through the side wall of the module  65 . The position of the shaft rotary seal  140  is important for the proper operation of the assembly  100  and, in this regard, the bore in the side wall of the module  65  in which the seal  140  is seated is precisely located relative to the machined outer surface of the module wall  104 , which thus also serves as a reference surface datum for the shaft rotary seal  140 . 
     As mentioned, it should be fully appreciated that the present invention also encompasses any manner of vacuum chamber module that incorporates one or more of the slit valve assemblies  100  as described herein. In a particular embodiment, the vacuum chamber module may be any one of the modules discussed above in  FIG. 1  wherein the module is an in-line component in a vacuum deposition processing line for the manufacture of solar panels. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.