Abstract:
A variable lot size load port assembly is described having a tool interface, a port door, a latch key, an advance plate, and an elevator. The tool interface extends generally in a vertical dimension and has an aperture. The port door has a closed position wherein the port door at least partially occludes the aperture. The latch key extends from the port door and is configured to mate with a latch key receptacle of a door of a front opening unified pod (FOUP). The advance plate is configured to support a front opening unified pod (FOUP) and translate between a retracted position and an advanced position. The elevator raises and lowers the advance plate to bring the latch key receptacle of the door of the FOUP into alignment with the latch key of the port door.

Description:
CLAIM FOR PRIORITY 
   The present application claims the benefit of earlier-filed and co-pending U.S. Provisional Patent Application 60/819,602, filed on Jul. 10, 2006, and entitled, “Variable Lot Size Load Port,” which is incorporated herein by reference in its entirety. 
   CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is related to U.S. patent application Ser. No. 11/774,750 and U.S. patent application Ser. No. 11/774,760, both of which are titled, “Variable Lot Size Load Port,” are filed on the same day as the present application, and are incorporated by reference herein. 

   BACKGROUND 
   The present invention relates generally to wafer handling systems. Processing of semiconductor wafers generally requires transportation of wafers from one process station to another. Due to the sensitivity of semiconductor devices to contamination by particulates, it has become common practice to transport wafers in enclosed containers, referred to as front opening unified pods (FOUPs). The term, “FOUP” is used herein to broadly refer to containers having a front opening that are configured to transport substrates to and from process tools. The FOUP door mates with a port door of a processing unit, and the doors are removed providing access by the processing equipment to wafers held within the FOUP. 
     FIG. 1  illustrates a conventional 300 mm FOUP  20 , which includes a mechanically openable FOUP door  22  and a shell  24 , which together, defines a sealed environment for storing one or more workpieces located therein. FOUP door  22  includes a front face  31  with two latch key receptacles  33 . 
     FIG. 2  illustrates a conventional 300 mm load port assembly  23  for transferring wafers between the FOUP  20  and a process tool  28 . Load port  23  attaches to the process tool by a box opener/loader-to-tool standard interface (BOLTS) plate  36  that has an aperture  18 . The load port  23  includes, among other things, a container advance plate  25  and a port door  26 . In order to transfer the workpieces between FOUP  20  and process tool  28 , FOUP  20  is manually or automatically loaded onto advance plate  25  so that front surface  31  of FOUP door  22  faces front surface  30   a  of port door  26  while FOUP  20  is seated on advance plate  25 . Port door  26  occludes aperture  18  when in the closed position illustrated in  FIG. 2 . 
   The front surface  30   a  of port door  26  includes a pair of latch keys  32  that insert into the corresponding latch key receptacles  33  of FOUP door  22  as FOUP  20  is advanced towards the port door  26 . An example of a door latch assembly within a FOUP door adapted to receive and operate with latch keys  32  is disclosed in U.S. Pat. No. 4,995,430, entitled “Sealable Transportable Container Having Improved Latch Mechanism,” which is assigned to the Asyst Technologies, Inc., and is incorporated in its entirety by reference herein. In order to latch FOUP door  22  to the port door  26 , FOUP door  22  is seated adjacent port door  26  so that vertically oriented latch keys  32  are received within latch key receptacles  33 . 
   In addition to decoupling FOUP door  22  from the FOUP shell, rotation of the latch keys  32  also locks the keys into their respective receptacles  33 ; coupling FOUP door  22  to port door  26 . A conventional load port includes two latch key  32 , each of which are structurally and operationally identical to each other. 
   Advance plate  25  often includes three kinematic pins  27 , or some other registration feature, which mate within corresponding slots on the bottom surface of FOUP  20  to define a fixed and repeatable position of the bottom surface of the FOUP on advance plate  25  and load port assembly  23 . 
   Referring to  FIG. 3 , advance plate  25  is translationally mounted to advance the FOUP  20  toward and away from the load port  30 . Once a FOUP  20  is detected on the advance plate  25  by sensors in the load port assembly, FOUP  20  is advanced toward load port  30  in the direction of arrow A-A until front surface  31  of FOUP door  22  is proximate front surface  30   a  of port door  26  so that the flange of FOUP  20  forms a proximity seal with BOLTS plate  36 . The proximity seal provides a small space between the BOLTS plate surrounding the port door and the FOUP shell flange at the front edge of the FOUP shell after the pod has advanced. This space allows air  19 , which is at a higher than ambient pressure within the process tool to sweep away any particulates and prevent particulates from coming to rest on the flange. The proximity seal also ensures that particulates and other contaminants cannot enter the tool or the FOUP. The higher than ambient pressure is provided by a filter/blower system (not shown) attached to process tool  28  ( FIG. 2 ). 
   It is desirable to bring the front surfaces of FOUP door  22  into contact with the front surface of port door  26  and maintain contact to trap particulates between the doors. Once the FOUP and port doors are coupled, horizontal and vertical linear drives within the load port assembly move the FOUP door  22  and port door  26  together into the process tool  28  so that wafers may thereafter be transferred between the interior of the pod  20  and interior of process tool  28 . In the open position, port door  26  is translated away from aperture  18  so that it no longer occludes aperture  18 . For example, port door  26  and FOUP door  22  may be moved in and then down alongside an interior surface of BOLTS plate  36 . 
   Regardless of the desired relative positions of the FOUP and port doors after FOUP advance, it is necessary to precisely and repeatably control this relative positioning to ensure proper transfer of the pod door onto the port door and to prevent particulate generation. In order to establish the desired relative positions, conventional load port assembly systems rely on the fact that the kinematic pins establish a fixed and known position of the FOUP on the load port assembly so that, once seated on the kinematic pins, the FOUP may simply be advanced toward the load port a fixed amount to place the front surfaces of the respective doors in the desired relative positions. 
   Many of the components of the load port  30 , such as the BOLTS plate aperture  18 , the port door  26  and the container advance plate  25 , are fixed components—cannot be adjusted. A 300 mm load port  30  is designed to operate only with 300 mm pods  20 . Thus, there is a need for a load port that can accommodate and operate with various sizes of FOUPs. 
   SUMMARY 
   Broadly speaking, the present invention overcomes various limitations of existing load ports by providing a variable lot size load port as described herein. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below. 
   In one embodiment, a variable lot size load port assembly is provided having a tool interface, a port door, a latch key, an advance plate, and an elevator. The tool interface extends generally in a vertical dimension and has a front surface facing a front of the tool interface, a back surface generally parallel to the front surface, and an aperture. The port door has a closed position wherein the port door at least partially occludes the aperture and an open position wherein the aperture is substantially unobstructed by the port door. The latch key extends from the port door and is configured to mate with a latch key receptacle of a door of a front opening unified pod (FOUP). The advance plate positioned to the front of the tool interface below the aperture and extends generally horizontally. The advance plate is configured to support a front opening unified pod (FOUP) and translate between a retracted position and an advanced position, the advanced position being proximate the tool interface and the retracted position being spaced from the tool interface. The elevator raises and lowers the advance plate to bring the latch key receptacle of the door of the FOUP into alignment with the latch key of the port door. In this manner, a plurality of FOUPs of varying capacities, each having a latch key receptacle at a different elevation can be accommodated by the variable lot size load port assembly by varying an elevation of the advance plate. 
   In another embodiment, a variable lot size load port assembly includes a tool interface, an advance plate, and an upper and lower seal plate. The tool interface extends generally in a vertical dimension and has a front surface facing a front of the tool interface, a back surface generally parallel to the front surface, and an aperture. The advance plate is positioned to the front of the tool interface and below the aperture. The advance plate extends generally horizontally to support a front opening unified pod (FOUP) and is configured to translate between a retracted position a advanced position, the advanced position being proximate the tool interface and the retracted position being spaced from the tool interface. The upper seal plate has an upper end secured to the tool interface and a lower end covering a portion of the aperture, the upper seal plate being shaped to form a proximity seal with a front flange of the FOUP. The lower seal plate has a lower end secured to the tool interface and an upper end covering a portion of the aperture, the lower seal plate being shaped to provide a proximity seal with the front flange of the FOUP, the upper seal plate and the lower seal plate occluding upper and lower portions of the aperture to form a reduced aperture. 
   In yet another embodiment, a variable lot size load port assembly includes a tool interface, a port door, a latch key, an advance plate, and a replaceable static plate. The tool interface extends generally in a vertical dimension and has a front surface facing a front of the tool interface, a back surface generally parallel to the front surface, and an aperture. The port door has a closed position wherein the port door at least partially occludes the aperture and an open position wherein the aperture is substantially unobstructed by the port door. The latch key extends from the port door to mate with a latch key receptacle of a door of a front opening unified pod (FOUP). The advance plate is positioned to the front of the tool interface and below the aperture, extending generally horizontally. The advance plate is configured to support a front opening unified pod (FOUP) and translate between a retracted position a advanced position, the advanced position being proximate the tool interface and the retracted position being spaced from the tool interface. The replaceable static plate is mounted to the tool interface and occludes a perimeter portion of the aperture, the static plate having a reduced aperture, the reduced aperture having a size and shape to form a proximity seal with a FOUP of a selected capacity. 
   The advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of an embodiment of a FOUP, according to the prior art; 
       FIG. 2  is an isometric view of one embodiment of a load port, according to the prior art; 
       FIG. 3  is a side elevation view of the load port shown in  FIG. 2 , illustrating various components of the load port in a cross-sectional view; 
       FIG. 4  is a front view of one embodiment of a load port; 
       FIG. 5A  is a side cross-sectional view of the load port shown in  FIG. 4 ; 
       FIG. 5B  is a detail of an upper portion of  FIG. 5A ; 
       FIG. 6  is a front view of another embodiment of a load port; 
       FIG. 7  is a schematic view an embodiment of a load port; 
       FIG. 8  is a front view of an embodiment of a port door; 
       FIG. 9  is a side view of the port door shown in  FIG. 8  in operation with a small capacity container; 
       FIG. 10  is a front view of another embodiment of a port door; 
       FIG. 11  is a schematic view of an embodiment of a load port, illustrating the port door shown in  FIG. 10  in operation with a large capacity container; 
       FIG. 12  is a front view of yet another embodiment of a port door; 
       FIG. 13  is a side view of the port door shown in  FIG. 12  in operation with a small capacity container; 
       FIG. 14  is a front view of the port door shown in  FIG. 12  adapted for use with a large capacity container; 
       FIG. 15  is a side view of the port door shown in  FIG. 14  in operation with a large capacity container; 
       FIG. 16  is a perspective view of various embodiments of a static seal plate; 
       FIG. 17  is an isometric view of various embodiments of port door extension plates; 
       FIG. 18  is a schematic view of another embodiment; 
       FIG. 19  is a schematic view of yet another embodiment; 
       FIG. 20  is a schematic view of the load port shown in  FIG. 19 , with an optional filter attached to the port door; 
       FIG. 21  is a schematic view of still another embodiment; 
       FIG. 22  is a schematic view of yet another embodiment; 
       FIG. 23  is a schematic view of another embodiment; 
       FIG. 24  is a schematic view of the load port shown in  FIG. 23 , in operation with a small capacity container; 
       FIG. 25A ,  FIG. 25B  and  FIG. 25C  are a schematic views of embodiments having a port door with retractable, repositionable or multiple latch keys; 
       FIG. 26  is a schematic view of another embodiment; 
       FIG. 27A  is a schematic view of the load port shown in  FIG. 26  in operation with a small capacity container; 
       FIG. 27B  is a schematic view of an alternate embodiment of the load port shown in  FIG. 27A ; and 
       FIG. 28  is a schematic view of the load port shown in  FIG. 27A , illustrating the small capacity container coupled to the port door. 
   

   DETAILED DESCRIPTION 
     FIGS. 4-6  illustrate a variable lot size load port  100  with static seal plates. In this embodiment, the load port  100  includes, among other things, a tool interface  102  having an aperture  104  and a container advance assembly  106 . In one embodiment, tool interface  102  conforms to industry standards for a Box Opener/Loader to Tool Standard (BOLTS) interface, commonly referred to as a “BOLTS interface” or a “BOLTS plate.” In one embodiment, the aperture  104  is sized to allow 300 mm wafers to pass through. A conventional tool interface  102  is preferably uniform in thickness. Here, the tool interface  102  has been modified to accept various sizes of seal plates for the purpose of adapting the tool interface to different capacity FOUPs as described in further detail below. In this embodiment, tool interface  102  has been machined to form a recessed surface  103 , which provides a mounting surface for each seal plate (as described in more detail later). 
     FIG. 4  illustrates that the tool interface  102  includes a beveled surface that transitions into a recessed surface  112 .  FIGS. 5A and 5B  show a cross section of the tool interface  102  in  FIG. 4 . The recessed surface  112  defines the perimeter of the plate aperture  104 . Even though the  FIGS. 4-5  embodiment of the load port  100  is designed to operate with a large capacity FOUP, a static seal plate  108  is mounted to the recessed surface  103 . In one embodiment, the large capacity FOUP, contains, e.g., 25 wafers or substrates. In contrast, the small capacity FOUP described below with reference to  FIGS. 6 and 7 , can hold at most fewer wafers or substrates than the large capacity FOUP, e.g., 8 or 10 wafers or substrates. The smaller capacity FOUP is suitable for instances where smaller lot sizes are used, each lot size being a number of wafers or substrates being processed as a group. The small capacity FOUPs can therefore save considerable storage space when compared to using standard 25-wafer FOUPs for the smaller lot sizes, in which case each large capacity FOUP may be more than half empty. 
   To “reconstruct” the plate aperture  104  back into a uniform structure, the seal plate  108  includes its own beveled surface  110 ′ that transitions to a recessed surface  112 ′. In a preferred embodiment, the beveled surfaces  110  and  110 ′, and the recessed surfaces  112  and  112 ′ are flush. The seal plate  108  may be affixed to the tool interface  102  with any type of fasteners (e.g., bolts, screws, etc.) or by other means (e.g., welded to the BOLTS plate).  FIG. 4  illustrates that the plate aperture  104  has a height H 1  and a width W 1 , which in a preferred embodiment, corresponds to the height and width of a conventional load port aperture. 
     FIG. 6  illustrates a seal plate  116 . The seal plate  116 , similar to the seal plate  108 , is mounted to the recessed surface  103  of the tool interface  102 . The seal plate  116  is used when the load port  100  operates with a small capacity FOUP  40  ( FIG. 7 ). In this embodiment, the seal plate  116  includes a top portion  124  that mounts to the recessed surface  103  of the tool interface  102 , and a distal end  125  that extends into the aperture  104 . To “reconstruct” the plate aperture  104  to a size for accommodating a small capacity FOUP  40 , the seal plate  116  includes its own beveled surface  120  that transitions to a recessed surface  122 . In a preferred embodiment, the recessed surface  112  of the tool interface  102  and the recessed surface  122  of the seal plate  116  are flush. Similarly, the recessed surface  112  of the tool interface  102  and the recessed surface  122  of the seal plate  116  are preferably flush. The seal plate  116  may be affixed to the recessed surface  103  of the tool interface  102  with any type of fasteners (e.g., bolts, screws, etc.) or by other means (e.g., welded to the BOLTS plate). The tool interface  102  is not required to have a beveled and recessed surface. However, as shown in  FIG. 7 , the recessed surfaces  112 ,  122  allow FOUP  40  to move farther forward, which may be desirable. 
   The seal plate  116  reduces the size of the plate aperture  104  to operate with a small capacity FOUP  40 .  FIG. 6  illustrates that the height of the plate aperture  104  has been reduced to a height H 2 . When the seal plate  116  is affixed to the recessed surface  103  of the tool interface  102 , the seal plate  116  effectively seals off the portion of the aperture  104  located above the recessed surface  122 . In this embodiment, the width of the plate aperture remains at the same width W 1 , which corresponds to the width of a conventional load port aperture. The seal plate  116  may also reduce the width W 1  of the plate aperture  104 . 
     FIG. 7  provides a schematic representation of a small capacity FOUP  40  in operation with the load port  100  shown in  FIG. 6 . In this embodiment, a small capacity FOUP  40  is seated on the container advance assembly  106  and has been advanced towards the tool interface  102  to a position where the FOUP shell  44  makes a proximity seal with the recessed surface  122  of the seal plate  116  and the recessed surface  112  of the tool interface  102 . The sealing plate  116  effectively seals off, or covers a portion of, the plate aperture  104 . The seal plate  116  reduces the amount of exposure the interior of the processing tool has to the outside environment. 
     FIGS. 8-11  illustrate one embodiment of a port door  126  that may retain and remove both a small capacity FOUP door  42  and a large capacity FOUP door  22 . The height of a large capacity FOUP door  22  is not the same as the height of a small capacity FOUP door  42 . For one pair of latch keys  132  to operate with both types of FOUP doors, the latch keys  132  extending from the port door  126  cannot engage the center of both FOUP doors. The latch keys  132  preferably extend from the port door face  130  at an elevation between the center of the small capacity FOUP door  42  and the large capacity FOUP door  22 . Here, the latch keys  132  are placed as high up on the port door face  130  as possible that is within the height of the small capacity FOUP door  42 .  FIG. 8  illustrates that the latch keys  132  extend from the port door  126  at an elevation above the centerline CL 1  of the port door face  130  (having a height H 3 ). 
     FIG. 9  illustrates the port door  126  in operation with a small capacity FOUP  40 . The FOUP door  42  includes latch key receptacles (not shown in  FIG. 9 ) that align with the latch keys  132  when the FOUP is seated on a container advance assembly. As shown, the latch keys  132  do not engage the center of the FOUP door  42 .  FIG. 10  illustrates the port door  126  adapted to operate with a large capacity FOUP  20 . The port door  126 , in this embodiment, includes an extension plate  140 . The extension plate  140  is preferably flush with the port door face  130 , and may be secured to the port door  126  by any fastening devices known within the art. The height H 5  of the extension plate  140  increases the effective height of the port door face  130  to a height H 4 . In a preferred embodiment, the height H 4  is substantially similar to the height of a large capacity FOUP door  22 . 
     FIG. 11  illustrates the port door  126  in operation with a large capacity FOUP  20 . In particular,  FIG. 11  illustrates that the port door face  130  and extension plate face  142  are substantially the same height (and surface area) as the FOUP door face  31 . The latch key receptacles in the FOUP door  22 , in this embodiment, are located below the center of the FOUP door in order to align with the latch keys  132  extending from the port door  126 . After the latch keys  132  retain the FOUP door  22 , the port door  126  moves the FOUP door  22  into the tool (shown in hidden lines). 
   If the port door  126  did not have the extension plate  140 , an upper portion of the large capacity FOUP door face  31  would be exposed when the port door  126  is coupled to the FOUP door  22 . If this upper surface of the FOUP door  22  was contaminated with particles, these particles could detach from the FOUP door  22  and possibly contaminate wafers being transferred between the FOUP  20  and the process tool. The extension plate  140  therefore traps particles on the FOUP door face  31  and prevents the particles from entering into the tool. The port door  126  with an extension plate  140  may also be used to retain and remove a small capacity FOUP door  42 . When the port door  126  engages a small capacity FOUP door  42 , the face  142  of the extension plate  140  will be exposed. The extension plate face  142  may have particles or contaminants on it that will not be trapped or contained by the FOUP door  42 . But because the exposed face  142  of the extension plate  140  will face towards the interior of the tool interface  102  after the port door  126  and FOUP door  42  is lowered into the process tool, the opportunity for contaminating wafers is small (compared to having the exposed face of a FOUP door in the process tool). 
     FIGS. 12-15  illustrate another embodiment of a port door  126  that may also operate with both a large capacity FOUP  20  and a small capacity FOUP  40 . Again, the height of a large capacity FOUP door  22  shown in  FIG. 15  is not the same as the height of a small capacity FOUP door  42  shown in  FIG. 13 . In contrast to the  FIG. 8  embodiment, latch keys  132  extending from the port door  126  engage the center of both types of FOUP doors. The latch keys  132  extend from the centerline CL 1  of the port door face  130 .  FIG. 13  illustrates the port door  126  in operation with a small capacity FOUP  40 . The FOUP door  42  includes latch key receptacles (not shown in  FIG. 9 ) that align with the latch keys  132  when the FOUP is seated on a container advance assembly. Thus, the latch keys  132  engage the center of the FOUP door  42 . 
     FIG. 13  also illustrates that the container advance assembly  106  has elevated the small capacity FOUP  40  (e.g., the center of the FOUP is higher than the standard 900 mm height), so that its latch key receptacles (not shown) are aligned with the latch keys  132 . By way of example only, the port door  126  shown in  FIG. 13  is a component of a load port that includes the seal plate  116 ′ (as shown in  FIG. 16 ). 
   The container advance assembly  106  may be vertically adjusted either automatically or manually by way of an elevator in order to align the latch key receptacles in the FOUP door  42  with the latch keys  132 . In one embodiment, the elevator comprises an adapter  107  that may be manually added between the container advance assembly  106  and the container advance assembly  106  (as shown in  FIG. 13 ). The adapter  107  may have precise features so that no adjustments are required after it is attached to the support plate  106 . 
   Alternately, the container advance assembly  106  may be mounted to an automated elevator. For example, the load port may comprise a Direct Loading Tool, as disclosed in U.S. application Ser. No. 11/177,645, which is assigned to Asyst Technologies, Inc., and is incorporated in its entirety by reference herein. In this case, the Direct Loading Tool automatically adjusts the elevation of the container advance assembly  106  depending on whether the FOUP is a small capacity FOUP  40  or a large capacity FOUP  20 . 
     FIGS. 14-15  illustrates the port door  126  adapted to operate with a large capacity FOUP  20 . The port door  126 , in this embodiment, includes a first extension plate  144  and a second extension plate  146 . The face  148  of the extension plate  144  and the face  150  of the extension plate  146  are each preferably flush with the port door face  130 . Each extension plate  144  and  146  may be secured to the port door  126  by any fastening devices known within the art. The height H 6  of the first extension plate  144  and the height H 7  of the second extension plate  146  increases the effective height of the port door face  130  to a height H 4 . In a preferred embodiment, the height H 4  is substantially similar to the height of a large capacity FOUP door  22 . 
     FIG. 15  illustrates the port door  126  in operation with a large capacity FOUP  20 .  FIG. 14  illustrates that the port door face  130 , with the extension plates  144  and  146 , are substantially the same height (and surface area) as the FOUP door face  31 . The latch key receptacles in the FOUP door  22  are located at the center of the FOUP door  22  in order to align with the latch keys  132  extending from the port door  126 . After the latch keys  132  retain the FOUP door  22 , the port door  126  moves the FOUP door  22  into the tool. 
     FIGS. 16-17  illustrate other embodiments of a static seal plate. In these embodiments, each seal plate comprises a single plate with an opening sized to accommodate either a small capacity FOUP or a large capacity FOUP. Although not depicted here, each seal plate  116 ′ or  116 ″ may include recessed shoulders at the perimeters of apertures  118 ′ and  118 ″, e.g., as shown in  FIG. 26  at  616  and  614 .  FIG. 16  illustrates the tool interface  102  with a plate aperture  104 . The static seal plate  116 ′ would be used when the load port will operate with a small capacity FOUP  40 . The seal plate  116 ′ mounts to the tool interface  102  within the plate aperture  104  by any means known within the art (e.g., bolts). The seal plate  116 ′ reduces the size of the plate aperture  104  down to the size of the opening  118 ′. In this embodiment, the aperture  118 ′ is located in the center of the seal plate  116 ′. The aperture  118 ′ can be located in other locations in the seal plate  116 ′.  FIG. 16  also illustrates a static seal plate  116 ″. The seal plate  116 ″ would be used when the load port will operate with a large capacity FOUP. The seal plate  116 ″ mounts to the tool interface  102  within the plate aperture  104 , and thus reduces the size of the aperture  104  to the size of the aperture  118 ″. The aperture  118 ″ in the seal plate  116 ″ is centered in the seal plate  116 ″. The aperture  118 ″ may, of course, be located anywhere in the seal plate  116 ″. In a preferred embodiment, the height and width of the seal plates  116 ′ and  116 ″ are identical so that the plates may be easily interchanged. 
     FIG. 17  illustrates various embodiments of an extension plate  140  for the port door  126 . The extension plates  140 ′ and  140 ″ allow the port door  126  to operate with both a large capacity FOUP  20  and a small capacity FOUP  40 . The port door  126  includes a base  127  and a raised latch key housing  129 . The latch key housing  129 , which has a depth d 1 , has a smaller perimeter than the perimeter of the base  127 . The latch keys  132  extend from the latch key housing  129 . 
   The extension plate  140 ′ has a thickness d 2  and includes an aperture  128 ′. The thickness d 2  of the extension plate  140 ′ is preferably equal to the depth d 1  of the latch key housing  129 . Thus, the extension plate face  144 ′ is flush with the latch key housing face  131  when the extension plate  140 ′ is secured to the port door  126 . The surface area of the extension plate face  144 ′ (plus the housing face  131 ) is preferably the same or similar to the surface area of the FOUP door face  41 . The extension plate  140 ″ has a thickness d 3 , and includes an aperture  128 ″. The thickness d 3  of the extension plate  140 ″ is preferably equal to the depth d 1  of the latch key housing  129 . Thus, the extension plate face  144 ″ is flush with the latch key housing face  131  when the extension plate  140 ″ is secured to the port door  126 . The surface area of the extension plate face  144 ″ (plus the housing face  131 ) is preferably the same or similar as the surface area of the FOUP door face  31 . 
     FIGS. 18-25  illustrate various embodiments of an adjustable seal plate.  FIG. 18  illustrates a load port  200 . The load port  200  includes, among other things, a tool interface  202  with a plate aperture  204 , a seal plate  208 , a port door  226  and a container advance assembly  206 . The seal plate  208  comprises a vertically adjustable seal plate. The tool interface  202  underneath the aperture  204  includes a beveled surface  210  that transitions into a recessed surface  212 . The port door  226  shown in  FIG. 18  is similar to the port door  126  illustrated in  FIGS. 7 and 11 . However, the load port  200  is not limited to this port door configuration. 
   In operation, the small capacity FOUP  40  is placed on the container advance assembly  206 . The container advance assembly  206  moves the FOUP  40  towards the tool interface  202  to the position shown in  FIG. 18 . In this advanced position, the FOUP&#39;s top flange  43  is proximate to the port door  226  and the FOUP&#39;s bottom flange  45  is proximate to the recessed surface  212  of the plate (as shown in  FIG. 18 ). The FOUP door face  44  is also located proximate to the port door face  230 . The latch keys (not shown) then unlock and retain the FOUP door  42 . It is also possible for the flanges  43  and  45  and/or the FOUP door  42  to contact the port door  226 . 
   The port door  226 , when located in the closed position (as shown in  FIG. 18 ), occupies most of the aperture  204 . The seal plate  208  is adjustable relative to the tool interface  202  in the direction of the arrow  219 . The upper surface  231  of the port door face  230  is exposed to the ambient environment when the port door  226  is in the closed position and the seal plate  208  is located in an uppermost position (not shown). The seal plate  208  may be lowered to the position shown in  FIG. 18  after the FOUP  40  has been moved to the advanced position, before the FOUP  40  is moved to the advanced position or while the FOUP  40  is being moved to the advanced position. The seal plate  208  is preferably moved to the position shown in  FIG. 18  before the port door  226  is lowered into the tool. The seal plate  208  moves downward and forms a proximity seal with the top surface  43 ′ of the FOUP&#39;s top flange  43  and covers the upper surface  231  of the port door face  230 . 
   After the port door  226  retains the FOUP door  42 , the port door  226  removes the FOUP door  42  and moves itself and the FOUP door  42  into the tool. The seal plate  208  preferably remains in the lowered position while the wafers are processed; preventing particles from entering into the tool. The seal plate  208  effectively reduces the size of the plate aperture  204 . After the FOUP door  42  is returned to the FOUP  40 , the container advance assembly  206  moves the FOUP  40  away from the tool interface  202 . If the next FOUP placed on the assembly  206  is the same size, the seal plate  208  may remain in the lowered position. Or the seal plate  208  may retract in the direction  219 , and is then lowered when the next FOUP is moved to the advanced position. The adjustable seal plate  208  may form a proximity seal with any size FOUP simply by being lowered proximate to the FOUP shell. Thus, the load port  200  may operate with various size FOUPs. One disadvantage to the load port  200  shown in  FIG. 18  is that the port door  226  may strike the FOUP&#39;s top flange  43  when the port door  226  mates with the FOUP door  42 . 
     FIG. 19  illustrates the load port  200  with another embodiment of an adjustable seal plate  208  and a port door  226 . In this embodiment, the seal plate  208  includes a planar surface  212   a , and a beveled surface  215  that transitions into a recessed surface  213 . The seal plate  208  moves vertically with respect to the tool interface  202  (as shown by arrows in  FIG. 19 ). The seal plate  208  forms a proximity seal with the front face  46  of the FOUP&#39;s top flange  43  when the FOUP  40  is located in the advanced position (as shown in  FIG. 19 ). The FOUP&#39;s lower flange  45  forms a proximity seal with the recessed surface  212  of the tool interface  202 . The proximity seals allow some air  19  to escape from the back side of tool interface  202 , which is maintained at a higher than ambient pressure, thereby preventing particles and other contaminants from entering the process tool. 
   In operation, the FOUP  40  is placed on the container advance assembly  206 . While the port door  226  is located in a closed position (as shown in  FIG. 19 ), the FOUP  40  is moved forward to the position shown in  FIG. 19 . The seal plate  208  moves downward towards the FOUP  40  until the recessed surface  213  is located in front of, or adjacent to, the front surface  46  of the FOUP&#39;s upper flange  43 . In a preferred embodiment, the seal plate  208  does not contact the port door  226 . The air velocity through this proximity seal is preferably high enough to insure that any particle located on the FOUP shell&#39;s front surface  46  would be swept into the ambient environment and not into the tool. 
   To accommodate the seal plate&#39;s beveled surface  215  and recessed surface  213 , the upper section  242  of the port door  226  has a recessed surface  243 . The recessed surface  243  is set back from the port door face  230 . A port door face typically covers substantially the entire FOUP door face when the port door and FOUP door are coupled to trap the particles on the FOUP door and port door.  FIG. 19  illustrates that the port door face  230  does not cover the entire FOUP door face  31  when the port door  226  retains the FOUP door  42 . Thus, the port door  226  does not strike the FOUP&#39;s top flange  43 . The recessed face of the port door creates a gap g 1  between the port door&#39;s recessed surface  243  and the FOUP door face  31 . The Gap g 1  is preferably as small as possible. The gap g 1  is determined by the thickness of the tool interface  202  and the seal plate  208 . Thus, the thickness of the seal plate  208  and the tool interface  202  are preferably as thin as possible to minimize the distance g 1  between the port door face  243  and the FOUP door face  31 . 
   Even though the recessed surface  243  and the FOUP door face  31  are not flush when the port door  226  is coupled to the FOUP door  42 , any particles on the exposed portions of the port door  226  or FOUP door  42  should not cause contamination of the wafers stored in the FOUP  40 . The laminar flow of clean air traveling within the process tool typically travels vertically from the top of the tool to the bottom of the tool. After the port door  226  moves the FOUP door into the tool, this laminar air flow will prevent the particles within the gap g 1  from migrating upwards to the wafers W. In addition, the port door&#39;s upper section  242  provides a barrier preventing particles within the gap g 1  from moving directly into the interior of the tool&#39;s clean area. The port door&#39;s upper section  242  basically shields the FOUP door face  31  from local air turbulence that could dislodge particles on the FOUP door face  31 . 
     FIG. 20  illustrates a blower system  280  that may be incorporated into the port door  226 , which is shown latched to port door  226  at an intermediate position between the open position and the closed position. The blower system  280  improves the cleanliness of the portion of the port door  226  that is exposed to the outside or ambient environment. The blower system  280 , in this embodiment, includes a blower or fan  282  attached to a housing  284  with an inlet  286 , and a filter  288  for filtering the air before it enters the housing  284 . The blower system  280  creates an air flow (as shown by arrows in  FIG. 20 ). 
   The exit  290  of the blower housing  284  preferably comprises a perforated or porous surface so that gas (e.g., air, nitrogen, etc.) exits the housing and travels towards the outside environment. The filter  288  may comprise a removable module or an integral part of the blower system  280 . Other devices for creating air flow are also possible. By forcing clean air out of the housing  284  through the exit surface  290  (see arrows), the number of particles that attach to the exit surface  290  is minimized, thereby reducing contamination of the clean area inside the process tool. Alternatively, air may be pulled into the housing  284  (opposite direction of arrows shown in  FIG. 20 ) through the exit surface  290 , also minimizing the number of particles entering into the tool. 
   The blower system  280  does not require a fan  282  or a filter  288 . The cleanliness of the exit surface  290  may rely solely on the air flow created by the higher pressure gas within the processing tool exiting into the outside environment. When the exit surface  290  of the blower housing  284  is exposed to the outside environment, and therefore susceptible to particle contamination, the pressure differential would force the clean air from within the process tool through the exit surface  290  and to the outside environment. 
     FIGS. 21-22  illustrate yet another embodiment of an adjustable seal plate. The load port  300  includes, among other things, a plate  302  with an aperture  304 , a seal plate  308 , a container support assembly  306  and a port door  326 . 
     FIG. 21  illustrates the load port  300  in operation with a large capacity FOUP  20 . The seal plate  308 , in this embodiment, includes a stationary plate  310  and an adjustable plate  312 . The adjustable plate  312  includes a recessed surface  322 . The stationary plate  310  includes a recessed surface  314 . The adjustable plate  312  moves vertically (shown by arrows) with respect to the plate  302 . Moving the adjustable plate  312  controls the size of the plate aperture  304 . The stationary plate  310  may also comprise a machined surface of the plate  302 . 
   The adjustable plate&#39;s recessed surface  322  forms a proximity seal with the FOUP&#39;s upper flange  43 . The recessed surface  314  of the stationary plate  310  forms a proximity seal with the FOUP&#39;s lower flange  45 .  FIG. 21  illustrates that the surface area of the port door surface  330  is not equivalent to the surface area of the FOUP door  22  even though the height of the port door is substantially equivalent to the height of the FOUP door. To accommodate the seal plate  308 , the port door  326  includes a contact surface  330 , a first recessed surface  346  and a second recessed surface  348 . The latch keys (not shown) extend from the port door contact surface  330 . The latch key receptacles in the FOUP door  22  (not shown) are preferably aligned with the latch keys while the FOUP is seated on the container advance assembly  306 . 
   In operation, the FOUP  20  is seated on the container advance assembly  306  and the container advance assembly  306  moves the FOUP to an advanced position (as shown in  FIG. 21 ). At this position, the FOUP&#39;s lower flange  45  makes a proximity seal with the recessed surface  314  of the stationary plate  310 . The adjustable plate  312  moves downward towards the FOUP  20  until the recessed surface  322  makes a proximity seal with the FOUP&#39;s upper flange  43 . The latch keys unlock and retain the FOUP door  22 , and preferably pulls the FOUP door into contact with the contact surface  330 . The port door contact surface  330  and the FOUP door face  31  are not required to be in direct contact with each other. The port door&#39;s recessed surfaces  346  and  348  are separated from the FOUP door face  31  by a distance d 4 . The distance d 4  may vary. The distance d 4  simply must be wide enough to allow the seal plate  308  to fit between the port door and the FOUP door. 
     FIG. 22  illustrates the load port  300  in operation with a small capacity FOUP  40 . To accommodate a small capacity FOUP  40 , the port door  326  has been lowered (compared to the position shown in  FIG. 21 ) by way of z-axis actuator  327  until the latch keys align with the FOUP&#39;s latch key receptacles (which are preferably in the center of the FOUP door  42 ). Z-axis actuator  327  may be, for example, a lead-screw actuator for raising and lowering port door  326  to align latch key receptacles for a FOUP of a selected capacity. In one embodiment, z-axis actuator  327  is also used for moving port door  326  from the open and closed position, wherein when closed, the port door  326  at least partially occludes aperture  104  and when open, the aperture is substantially unobstructed by the port door, e.g., by lowering the port door to a position below and behind aperture  104 . A y-axis actuator  329  is used to move port door (along with a FOUP door) into the interior of the process tool so that both the FOUP door and port door can be lowered without crashing into the BOLTS plate. 
   In the position shown in  FIG. 22 , the lower section  344  of the port door overlaps both the plate  302  and the stationary plate  310 . The FOUP&#39;s lower flange  45  still forms a proximity seal with the stationary plate&#39;s recessed surface  314 . The adjustable plate  312  moves downward until the recessed surface  322  forms a proximity seal with the FOUP&#39;s upper flange  43 . The adjustable plate  312  effectively reduces the height of the plate aperture  304  to substantially the height of the FOUP  40  to prevent particles from entering into the tool  11 . In this embodiment, the need for the port door&#39;s recessed surfaces is more apparent. The adjustable plate  312  translates between the FOUP&#39;s upper flange  43  and the port door&#39;s recessed surface  346 . The stationary plate&#39;s recessed surface  314  fits between the FOUP&#39;s lower flange  45  and the port door&#39;s recessed surface  348 . 
   In one embodiment, the port door&#39;s recessed surfaces  346  and  348  may comprise a perforated or porous surface. A perforated or porous surface would allow clean air to flow through each recessed surface to help minimize the amount of particles collected on the surfaces  346  and  348 . Any device such as, but not limited to, a fan, a filter or the greater differential pressure from inside the process tool enclosure  11  may provide the necessary air flow. 
     FIGS. 23-24  illustrate a load port  400 . The load port  400 , in this embodiment, includes a plate  402  with a plate aperture  404 , a container support assembly  406 , a seal plate  408  and a port door  426 . The seal plate  408  includes a stationary plate  410  having a recessed surface  414  and an adjustable plate  412  having a recessed surface  422 . The port door  426  includes a front surface  430 , and may include extensions  436  and  438  (as shown in hidden lines in  FIG. 23 ). The extensions  436  and  438 , in this embodiment, extend a length d 3  from the port door  426 . The extensions  436  and  438  may have other lengths. As will be described in more detail later, the adjustable plate  412  and the stationary plate  410  each form a proximity seal with the outer edge of the FOUP&#39;s upper flange  43  and lower flange  45  (as opposed to the front face of each flange as shown in the  FIGS. 21-22  embodiments). 
     FIG. 23  illustrates the load port  400  in operation with a large capacity FOUP  20 . In operation, a FOUP  20  is set on the container advance assembly  406 , which moves the FOUP  20  towards the plate  402 . When the FOUP  20  is in the position shown in  FIG. 23 , the stationary plate  410  forms a proximity seal with the FOUP&#39;s lower flange  45 . The adjustable plate  412  may be vertically adjusted until the recessed surface  422  forms a proximity seal with the FOUP&#39;s upper flange  43 . In this embodiment, the proximity seal between the seal plate  408  and the upper and lower flanges  43 ,  45  is formed with the outside surface of each flange—not the front surface of each flange (as shown in  FIG. 21 ). For example, the recessed surface  422  of the adjustable plate  412  forms a proximity seal with the outer or top surface  25 ′ of the upper flange  23 . The recessed surface  414  of the stationary plate  410  forms a proximity seal with the lower flange  45 . 
   In this embodiment, the port door  426  does not require any recessed surfaces to accommodate the adjustable plate  412  or the stationary plate  410 . The front surface  430  of the port door  426  may be substantially the same height and surface area as the FOUP door  22 . The port door  426  is more like a conventional port door, which will trap more particles between the port door front surface  430  and the FOUP door  22  when the FOUP door  22  and the port door  426  are coupled together. 
   The extension features  436  and  438  help prevent particles from entering into the process tool. Each extension plate overlaps slightly with the respective seal plate. The extension feature  436  overlaps slightly with the recessed surfaces  422  of the adjustable plate  412  to block or minimize air flow that will otherwise travel within the gap between the port door, the adjustable plate and the seal plate. The extension feature  438  overlaps slightly with the recessed surfaces  414  of the stationary plate  410  to block or minimize air flow that would otherwise travel within the gap between the port door, the stationary plate and the FOUP&#39;s lower flange  45 . The extension features  436  and  438  are shown as rectangular structures, but may comprise any shape. 
     FIG. 24  illustrates the load port  400  in operation with a small capacity FOUP  40 . The small capacity FOUP  40  is seated on the container advance assembly  406 . The load port  400  does not need to be modified when, for example, a large capacity FOUP is removed from the container advance assembly  406  and then a small capacity FOUP  40  is placed on the container advance assembly, or vice versa. The surface area of the port door&#39;s front surface  430  is greater than the surface area of the port door  42 . The port door&#39;s front surface  430  overlaps the recessed surface  422  of the adjustable plate  412  and the recessed surface  414  of the stationary plate  410  when the FOUP  40  is located in the advanced positions. 
   The seal plate  408  operates in the same manner as described in the  FIG. 23  embodiment above. Once the FOUP  40  is moved to the position shown in  FIG. 24 , the outer surface  45 ′ of the lower flange  45  forms a proximity seal with the recessed surface  414  of the stationary plate  410 . The adjustable plate  412  may be adjusted downward until the recessed surface  422  forms a proximity seal with the outer surface  43 ′ of the upper flange  43 . 
     FIG. 25A  illustrates a port door  526  with two sets of latch keys  432 . The latch keys  432  are shown extending from the port door  526  at an elevation A and an elevation B. In this embodiment, only one set of latch keys  432  extend from the port door  526  at either elevation A or elevation B—not both elevations. For example, each set of latch keys may comprise a pair, wherein only one latch key from each pair is visible in  FIG. 25A .  FIG. 25B  shows another embodiment in which a pair of latch keys  435  is repositionable from one pair of latch key receptacles at a first elevation and another pair of latch key receptacles at a second elevation.  FIG. 25C  shows yet another embodiment wherein latch keys  432  extend from the port door  426  at two different elevations at all times. 
   Referring to  FIG. 25A , elevation A corresponds to a preferred elevation when the load port  400  operates with a large capacity FOUP  20  (not shown in  FIG. 25 ). Elevation B corresponds to a preferred elevation when the load port  400  operates with a small capacity FOUP  40 . For example, elevation A may align with the vertical centerline of a large capacity FOUP door when a large capacity FOUP (see, for example,  FIG. 3 ) is seated on the assembly  406 . Likewise, elevation B may align with the vertical centerline of a small capacity FOUP door when a small capacity FOUP  40  is seated on the assembly  406 . The vertical centerline for each FOUP door is the line extending in a horizontal direction that is positioned at midpoint between the top and the bottom of the FOUP door. 
   If only one set of latch keys  432  extend from the port door  426 , the latch keys  432  may be moved between elevation A and elevation B either manually or automatically. In the automatic configuration shown in  FIG. 25A , the pair of latch keys  432  may be extended or retracted by a mechanism  433 . For example, latch key mechanism  433  in the port door  426  may be connected to a pivot mechanism (not shown) that would extend the pair of latch keys  432  at elevation A, and at the same time, retract the other pair of latch keys  432  at elevation B. 
   For manual configuration shown in  FIG. 25B , the port door  426  may include four receptacles  437 , each for receiving a latch key  435 . Two receptacles  437  may be located at elevation A and two receptacles  437  would be located at elevation B. When a large capacity FOUP  20  is seated on the advance plate  106 , a pair of latch keys  435  would be inserted into the receptacles  437  located at elevation A. If the next FOUP seated on the advance plate  106  is a small capacity FOUP  40 , then latch keys  435  would be manually removed (e.g., by an operator) from the receptacles  437  located at elevation A and inserted into the receptacles  437  located at elevation B, e.g., as indicated by the arrows. In one embodiment, a single latch key drive mechanism drives all four receptacles all the time, regardless of which receptacles the latch keys  432  are inserted into. Only the pair of latch keys  432  extending from the port door  426  would interface with the latch key holes in the FOUP door. 
   The port door  426  may also have four latch keys  432  extending from the port door at all times as shown in  FIG. 25C . A large capacity FOUP door would include four latch key receptacles for receiving the four latch keys. In one embodiment, only two of the four latch keys would operate at a time for unlocking and retaining the FOUP door. The other two latch keys would act as passive latch keys. If the pairs of latch keys are spaced far enough apart, a small capacity FOUP door may still only include two latch key receptacles, and only engage two of the four latch keys extending from the port door. 
   Each of the adjustable seal plates described above may also be used to prevent particles from contaminating the port door while the load port is waiting for a FOUP. A conventional load port, such as shown in  FIG. 2 , exposes the port door face  30  to the ambient environment while the load port is waiting for another FOUP. During this time, the port door  426  may collect contaminants or particles. To avoid or reduce port door contamination, the seal plate  208  shown in  FIG. 18  (for example) could be left in a lowermost position when there is no FOUP seated on the support assembly  206 . The seal plate  208  may be lowered until it contacts the recessed surface  210  of the tool interface  202 . In this position, the seal plate  208  covers the port door face  230  while the load port  200  is not in operation and prevents particles from contacting the port door face  230 . The seal plate  208  does not have to completely cover the port door face  230 . The seal plate  208  may be lowered to partially cover the port door face  230 . When a FOUP is loaded onto the support assembly  206 , the seal plate  208  would be raised to correspond to the size of the FOUP. 
     FIGS. 26-28  illustrate a load port  600 . The load port  600 , in this embodiment, includes a plate  602  with a plate aperture  604 , a container advance assembly  606  and a port door  626 . The plate  602  includes a recessed surface (shown as a bottom surface  614  and a top surface  616  in the cross-sectional view). The port door  626  includes at least one latch key  632  extending from its front surface  630 . In this embodiment, the container advance assembly  606  includes an elevator for vertical adjustment. A vertically adjustable container advance assembly allows the load port  600  to align the FOUP&#39;s latch key receptacles with the latch keys  632 . In one embodiment, the elevator is implemented using a lead screw mechanism  610  ( FIG. 26 ) for elevating container advance assembly  606 . Lead screw mechanisms are well known within the art; therefore no further description is required. Other elevator mechanisms including, but not limited to, linear actuators, belt drives, and so on, may also be used to elevate container advance assembly  606  vertically. 
     FIG. 26  illustrates the load port  600  in operation with a large capacity FOUP  20 . In operation, a FOUP  20  is set on the container advance assembly  606  (located at any height). If the FOUP&#39;s latch key receptacles are not aligned with the latch keys  632  when the FOUP  20  is set on the container advance assembly  606 , the lead screw mechanism  610  elevates the container advance assembly  606  until the FOUP&#39;s latch key receptacles are aligned with the latch keys  632 . The container advance plate  612  then moves the FOUP  20  horizontally towards the plate  602  until the FOUP&#39;s upper flange  43  and lower flange  45  each form a proximity seal with the plate  602 . The port door latch keys  632  unlock the FOUP door  22  and couple the FOUP door  22  to the port door  626 . The port door  626  then removes the FOUP door  22  from the FOUP  20 , and moves the FOUP door  22  into the tool. The wafers stored in the FOUP  20  may then be accessed. 
     FIG. 27A  illustrates the load port  600  in operation with a small capacity FOUP  40 . In this embodiment, a pair of proximity seal plates  618  and  620  have been secured to the plate  602  to decrease the height of the plate aperture  604 . Seal plate  618  is secured to the recessed surface  614  of the plate  602  by a fastener  625 . Seal plate  620  is secured to the recessed surface  616  of the plate  602  by a fastener  628 . The seal plates  618  and  620  may be secured to the plate  602  by other devices (e.g., bolt, screw, etc.) or may be permanently fastened to the plate  602 . If the seal plates  618  and  620  are temporarily fastened to the plate  602 , the load port  600  may be easily and quickly configured to operate with either a large capacity FOUP  20  or a small capacity FOUP  40  by adding and or removing the seal plates  618  and  620 . 
   In operation, a small capacity FOUP  40  is set on the container advance assembly  606  (located at any height). If the FOUP&#39;s latch key receptacles are not aligned with the port door latch keys  632  (as shown in  FIG. 27A ), the lead screw mechanism  610  moves the container advance assembly  606  upward until the FOUP&#39;s latch key receptacles are aligned with the port door latch keys  632  (as shown in  FIG. 28 ). At this point, the container advance plate  612  moves the FOUP  40  horizontally towards the plate  602 . 
   Small capacity FOUP  40  is advanced towards the plate  602  until the top of the FOUP&#39;s upper flange  43  of the front flange and the bottom of the lower flange  45  of the front flange each form a proximity seal with a seal plate. The top of upper flange  43  of the front flange forms a proximity seal with the distal end  624  of the seal plate  620 . The bottom of the lower flange  45  of the front flange forms a proximity seal with the distal end  622  of the seal plate  618 . It is possible for either the front surface or top surface of the upper flange  43  or front surface or bottom surface of lower flange  45  to form a proximity seal with the seal plates. 
   After the latch keys  632  insert into the FOUP door latch key receptacles, the latch keys  632  unlock the FOUP door  42  and couple the FOUP door  42  to the port door  626 . The port door  626  then removes the FOUP door  42  from the FOUP  40 , and moves the FOUP door  42  into the tool. 
   The lead screw mechanism  610  shown in  FIGS. 25-28 , or any other actuator known within the art, may be used in conjunction with the other container support or container advance assemblies shown in  FIGS. 4-25 . 
     FIG. 27B  shows an alternative to the embodiment of the load port shown in  FIG. 27A . In particular,  FIG. 27B  includes automated upper and lower seal plates  638  and  640  that retract into slots  650  and  652 , respectively. Automated upper and lower seal plates  638  and  640  are operated by automated actuators  646 ,  648 . Other configurations for the automated seal plates are possible, as would occur to those skilled in the art. 
   It should be appreciated that the above-described load ports and associated mechanisms for accommodating and operating with various size FOUPs are for explanatory purposes only and that the invention is not limited thereby. Having thus described a preferred embodiment of a method of operation and load port system, it should be apparent to those skilled in the art that certain advantages of the within system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. For example, the load ports and FOUPs have been illustrated and described in context of a semiconductor fabrication facility, but it should be apparent that many of the inventive concepts described above would be equally applicable to be used in connection with other non-semiconductor manufacturing applications.