Abstract:
A front opening wafer container suitable for large wafers such as 450 mm utilizes componentry with separate fasteners to lock the componentry together in an expedient manner providing robust connections and cost efficiencies. A container portion has an open front and receives on a bottom surface a base plate secured by twist lock connectors that also provide recesses for purge grommets. Kinematic coupling components readily and robustly lock onto the base plate. Interior wafer support components latch onto brackets on the side walls utilizing a separate locking insert with holding tabs and locking detents. A wafer retainer provides support and counters enhanced wafer sag associated with 450 mm wafers when the door is installed and seated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application a continuation of U.S. patent application Ser. No. 14/238,693, filed on Oct. 21, 2014, which is a 371 of PCT Application No. PCT/US2012/050624, filed Aug. 13, 2012, which claims the benefit to U.S. Provisional Patent Application No. 61/523,254, filed Aug. 12, 2011, all of which are incorporated herein in their entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to containers for sensitive substrates such as semiconductor wafers and in particular to components and assembly of the components into such containers. 
       BACKGROUND OF THE INVENTION 
       [0003]    Integrated circuits such as computer chips are manufactured from semiconductor wafers. These wafers are subjected to numerous steps during the process of making integrated circuits. This generally entails transporting a plurality of wafers from one workstation to another for processing by specialized equipment. As part of the processing procedure, wafers may be temporarily stored or shipped in containers to other plants or to end users. Such intra-facility and extra-facility movements may generate or expose the wafers to potential wafer ruining contaminants. In order to reduce the deleterious effect of contaminants on wafers, specialized containers have been developed to minimize the generation of contaminants and to isolate wafers from contaminants exterior to the containers. A principal feature common to these containers is that they are provided with removable doors or closures to enable access to the wafers inside. 
         [0004]    Plastic containers have been used for decades for transporting and storing wafers in-between process steps. Such containers have highly controlled tolerances for interfacing with processing equipment as well as the equipment/robots that transport the containers. Moreover, it is desirable in such plastic containers to use components that are attachable and removable without using metallic fasteners such as screws, since metal fasteners can cause particle generation when inserted and removed. 
         [0005]    Additional, required or desirable characteristics of containers to transport and/or store semiconductor wafers include light weight, rigidity, cleanliness, limited gaseous emissions, and cost effective manufacturability. The containers provide hermetic or close to hermetic isolation of wafers when the containers are closed. Simply stated, such containers need to keep the wafers clean, uncontaminated, and undamaged. Additionally, carriers need to maintain their capabilities under the rigors of robotic handling which includes lifting the carrier by the robotic flange positioned at the top of the container as well as transporting such carriers by way of conveyor systems that engage conveyor flanges on outside surface of side walls of the containers. 
         [0006]    Front opening wafer containers have become the industry standard for transporting and storing large diameter 300 mm wafers. In such containers the front door is latchable within a door frame of a container portion, and closes a front access opening through which the wafers are robotically inserted and removed. When the container is fully loaded with wafers the door is inserted into the door frame of the container portion and latched thereto. When seated, cushions on the door provide upward, downward, and inward constraint for the wafers. 
         [0007]    The semiconductor industry is now moving toward using even larger, 450 mm diameter, wafers. The larger diameter wafers, although providing cost efficiencies, also provide increased fragility, greater weight, and present undiscovered issues associated with handling and storing the larger wafers in containers made of plastic. Deflection and related problems associated with the expanses of plastic on the top, bottom, sides, front, and back are exacerbated. Assembly of larger components and the manufacturing tolerances of the components being assembled are more problematic. Forces exerted by the increased weight of substrates on the larger components cause more stress, manufacturing tolerances are greater and conventional connection techniques between components may be inadequate or not optimum. For example where in smaller wafer carriers where loads are transmitted from one component to another, often locking structure, such as detents, are putting directly on one component or the other. See, for example, U.S. Pat. No. 7,370,764, illustrating load bearing handles slidingly attachable to shells using detents integral with the handle. This patent is owned by the owner of the instant application. When dealing with greater weights and larger components such configurations may not be optimal. 
         [0008]    Wafers of larger dimensions also have significantly greater sag which will make them more susceptible to damage during handling and transport and require unique support not required for smaller wafers. This greater sag presents challenges in maintaining the desired spacing between wafers while still allowing placement and removal of the wafers robotically by robotic arms. 
         [0009]    In conventional 300 mm wafer containers, particularly those known as FOSBS (front opening shipping boxes) the front door is latchable to a container portion and closes a front access opening through which the wafers are robotically inserted and removed. When the container is fully loaded with wafers the door is inserted into the door frame of the container portion and latched thereto. In such a configuration the wafers have a first horizontal seating position on the laterally placed shelves and then, upon insertion of the door, the wafers are vertically elevated to a second seating position by wafer supports with angled ramps at the rear of the wafer container as well as wafer supports, often referred to as “cushions”, on the inside surface of the door. The container may then be rotated rearwardly 90 degrees to orient the wafers vertically for shipping. See U.S. Pat. Nos. 6,267,245 and 6,010,008 which are owned by the owner of the present application and which are hereby incorporated by reference. The angled ramps are part of V-shaped grooves, with the V rotated 90 degrees, whereby the lower leg of the V engages the wafer edge and rides up the inclination of the lower leg as the door is being inserted, ultimately seating at the inside apex of the V-shaped groove. When seated the cushions on the door then provide upward, downward, and inward constraint. With the greater sag associated with 450 mm wafers, conventional ramps as illustrated in U.S. Pat. No. 6,010,008 may not be optimal. 
         [0010]    Along with increasing size of semiconductor wafers, the density of the circuits formed on the wafers has also been increasing, making the circuits more susceptible to defects from smaller and smaller particles and other contaminants. In short, as wafers have increased in size, containers have increased in size as well, and the requirements for keeping the wafers clean and contaminant free have become more stringent due to the wafers being more susceptible to smaller particles and other contaminants. 
         [0011]    Accordingly, a need in the industry exists for a wafer container that addresses one or more of these problems, particularly as they exist relative to containers for 450 mm diameter and larger wafers. 
       SUMMARY OF THE INVENTION 
       [0012]    A front opening wafer container comprising a container portion and door particularly for large diameter wafers 300 mm and greater, particularly for 450 mm wafers, utilizes componentry with separate fasteners to lock the componentry together in an expedient manner providing robust connections and cost efficiencies. A container portion has an open front and receives on a bottom surface a base plate secured by twist lock connectors that also provide recesses for purge grommets. Kinematic coupling components readily and robustly lock onto the base plate. Interior wafer support components latch with brackets on the side walls and utilize a separate locking insert with holding tabs and locking detents. A wafer retainer provides support and counters enhanced wafer sag associated with 450 mm wafers when the door is installed and seated. 
         [0013]    A wafer retainer is removably attachable on an inside facing surface of the front door and comprises a pair of columns of cantilevered fingers that each depend from a vertical member. Each finger has a fixed or proximate end portion, an intermediate portion and a distal flexing end portion with a exposed wafer engaging surface facing into the wafer container. The finger initially extends horizontally from the vertical member and then at the intermediate portion and end portion extends slightly downward from the horizontal. The exposed wafer engaging surface has a linear recess or groove or valley defined by the junction of an upper surface portion and a lower surface portion. The groove or valley provides a wafer seating groove for when the door is fully seated in the door frame of the container portion. The wafer seating groove at the end portion of each finger is proximate the upper margin of the finger and extends to being approximately in the middle of the finger between the upper margin and lower margin as the wafer seating groove approaches the fixed end portion. The lower surface portion of the exposed wafer engaging surface being wider, in the vertical direction, at the distal end portion of each finger and then narrowing toward the fixed end portion. The wafer retainer further having additional column of fixed wafer seating portions in horizontal alignment with the wafer seating groove. 
         [0014]    As the door is inserted into the door frame of the container portion, front edges of the wafers will initially engage each finger, due to the sag of the wafers, at a lower point on the end portion of each finger. As the door is inserted further into the door frame the incline from vertical of each lower surface portion of each finger will urge the forward leading edge of each wafer upwardly, the horizontal extent of the engagement of each wafer with each finger will increase in horizontal width and extend closer to the fixed end portion of each finger as the door is further inserted until the door reaches its seated position. At such point, each wafer will be maximally engaged by the respective finger along most of the wafer engaging groove and will also be engaged by the additional column of fixed wafer seating portions. In an embodiment each wafer will be engaged by the door by two of the fingers and two additional fixed wafer seating portions. Thus, in an embodiment, there are two vertical columns of cantilevered wafer engaging fingers and two columns of fixed wafer seating portions. 
         [0015]    In an embodiment, wafer support shelves are secured to the side walls using a combination of cooperating brackets, that is, an insert portion and a pocket portion, one positioned on the shell and one on the back side of the wafer support shelf component, and a three part connection at the front side of the wafer support shelf component. The three part connection comprises a bracket on the wafer shelf component, a cooperating conforming bracket integral with the shell, and a locking member that secures the two brackets together. The locking member is configured as a clip with detents for retaining the clip in position. The clip secures the wafer shelf component to the shell. The detent that secures the components together is not on the two main components but on the component that connects and secures the together. Thus the latch that locks the third component together is substantially isolated for the two main components and substantially isolated from any load transfer between the components. Thus a feature and advantage of embodiments of the invention is a connection assembly for wafer shelves wherein the shelf component is engaged with the shell and a separate component maintains that engagement and has a detent that locks the separate component into a securement position by way of resilient integral tabs. 
         [0016]    Additionally, a base plate with kinematic couplings may also be secured utilizing additional fastener components including twist lock connectors that provides a robust connection of the base plate with minimal assembly, minimal particle generation, and allows use of the connections as purge ports. The base plate may utilize snap-in kinematic coupling components that readily and robustly and precisely attach to conforming apertures on the base plate. Again the connector secures the two principal components in engagement with one another such that the load transfer between the two components does not substantially extend through the connecter securing the components. 
         [0017]    Thus, a wafer container suitable for use with large wafers, including 450 mm wafers is presented with novel component configuration and attachment means. Said novelty provides enhanced performance, manufacturing expedience and reduced cost. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0018]      FIG. 1A  is a perspective view of a wafer carrier with embodiments of the inventions therein. 
           [0019]      FIG. 1B  is a perspective view of the wafer carrier of  FIG. 1A  with the door removed and illustrating attachment of components embodying the inventions herein. 
           [0020]      FIG. 1C  is a perspective view of the wafer carrier of  FIG. 1A  with the door removed and illustrating attachment of components embodying the inventions herein. 
           [0021]      FIG. 2  is a perspective view of the bottom side of a wafer carrier with embodiments of the inventions therein. 
           [0022]      FIG. 3  is a front elevational cross sectional view of a container portion of a wafer carrier with embodiments of the invention therein taken at line  3 - 3  of  FIG. 1C . 
           [0023]      FIG. 3A  is a detail cross sectional perspective view of portions of the cross section of  FIG. 3 . illustrating embodiments of the inventions. 
           [0024]      FIG. 3B  is a perspective view of a kinematic coupling component in accord with embodiments of the inventions therein. 
           [0025]      FIG. 3C  is a detailed side elevational cross sectional view of a container portion of a wafer carrier with embodiments of the invention therein taken at line  3 C- 3 C of  FIG. 1C , along the y-z plane. 
           [0026]      FIG. 4A  is a perspective view of a wafer support component in accord with embodiments of the inventions herein. 
           [0027]      FIG. 4B  is a perspective view of a locking clip in accord with embodiments of the inventions herein. 
           [0028]      FIG. 5A  is a perspective view of a shell of a container portion in accord with embodiments of the inventions herein. 
           [0029]      FIG. 5B  is a perspective view of the shell of  FIG. 5A  with a wafer support component inserted therein in accord with embodiments of the inventions herein. 
           [0030]      FIG. 5C  is a perspective view of the shell of  FIGS. 5A and 5B  with the wafer support component secured therein with a locking clip in accord with embodiments of the inventions herein. 
           [0031]      FIG. 5D  is a perspective view of a locking clip in accord with embodiments of the inventions herein. 
           [0032]      FIG. 5E  is a perspective view of an opposite side of the locking clip of  FIG. 5 d    in accord with embodiments of the inventions herein. 
           [0033]      FIG. 5F  is a perspective view of a wafer support component with a rearward bracket portion in accord with embodiments of the inventions herein. 
           [0034]      FIG. 5G  is a perspective view of a wafer support component with a forward bracket in accord with embodiments of the inventions herein. 
           [0035]      FIG. 5H  is a side elevational view inside the container portion illustrating the wafer support component secured to the shell with cooperating bracket in accord with the inventions herein. 
           [0036]      FIG. 6  is a perspective view of the wafer engaging side of a wafer restraint attachable to the inside surface of the front door in accord with embodiments of the inventions. 
           [0037]      FIG. 6A  is a perspective view of cantilevered fingers of the wafer restraint of  FIG. 6 . 
           [0038]      FIGS. 6B-6E  are side schematic views of the relative thicknesses and configurations of various cross sections of a cantilevered finger taken at the respective lines of  FIG. 6A . 
           [0039]      FIGS. 6F-6H  illustrate in schematic views in a plan view cross section taken at line  6 F- 6 F of  FIG. 6A  the progressive engagement of a wafer with a cantilevered finger in accord with embodiments of the inventions. 
           [0040]      FIG. 6I  is an elevational view of the inside surface of the front door with a wafer restraint in place in accord with embodiments of the inventions. 
           [0041]      FIG. 7A  is a perspective view of a twist lock connector that locks in less than one half turn in accord with embodiments of the inventions herein. 
           [0042]      FIG. 7B  is a perspective view of the twist lock connector of  FIG. 7A  from the opposite side and looking upwardly in accord with embodiments of the inventions. 
           [0043]      FIG. 7C  is a perspective view of a notch or groove on the twist lock connector of  FIG. 7A . 
           [0044]      FIG. 8  is a perspective view of the bottom side of a base plate with a boss unitary with the shell exposed therein in accord with embodiments of the inventions herein. 
           [0045]      FIG. 9A  is a perspective view of a shell of a container portion illustrating unitary bosses extending from the lower wall in accord with embodiments of the inventions. 
           [0046]      FIG. 9B  is a perspective view detailed view of a boss on the bottom of the shell of  FIG. 9A . For viewing convenience the shell has been inverted for this figure. 
           [0047]      FIG. 9C  is a perspective view detailed view of the boss of  FIG. 9B  with a twist lock connector in accord with embodiments of the inventions herein. 
           [0048]      FIG. 9D  is a cross sectional view of a elastomeric grommet with a check valve therein suitable for use in the connectors and bosses that are used as purge ports. 
           [0049]      FIGS. 10A and 10B  are views illustrating the attachment of a connector to a boss extending from a shell sandwiching the base plate therebetween. 
           [0050]      FIG. 10C  is a cross sectional view through a boss and twist lock connector with a purge grommet with a check valve shown in phantom in accord with embodiments of the inventions. 
       
    
    
     DETAILED DESCRIPTION 
       [0051]    Referring to  FIGS. 1A, 1B and 1C , a multiple application carrier (MAC)  30  is depicted in an embodiment of the invention. The MAC  30  comprises a container portion  32  generally having a shell  33  including an upper portion  36 , a top wall  37 , a lower portion  38 , a bottom wall  39 , two side portions  40 , two side walls  41 , a back wall  42 , and a back portion  45 . The upper portion  36 , lower portion  38  and the two side portions  40  extent toward a front opening  43  configured as a door frame  47  that can be closed and sealed with a door  44 . In one embodiment, the back portion  42  of the container portion  32  includes a plurality of brackets  46  configured as mounting pockets formed thereon. A pair of wafer support components  50  each have a pair of integrally molded cooperating brackets. The brackets cooperate with brackets on the shell. A locking clip may secure the wafer support component in place. A base plate  52  can be mounted proximate the lower portion  38  on the exterior of the container portion  32 . In one embodiment, the base plate  52  includes three kinematic coupling grooves component  56  and a plurality of twist lock connectors  58  that couple the base plate  52  to the lower portion  38  of the container portion  32 . The x-y-z coordinate system is illustrated in various figures for directional reference. 
         [0052]    Referring to  FIGS. 2 and 3 , the base plate  52  and the kinematic coupling groove component  56  of  FIG. 1C  are depicted in isolation. The kinematic coupling grooves component  56  are affixed to mounting apertures  62  on the base plate  52  and comprise a rim portion  64  and an apex portion  66  with a continuous, uninterrupted surface defined therebetween. In one embodiment, the rim portion  64  is substantially oval shaped with straight elongate sides  65  and half circular ends  66 . A pair of locking projection  68  can be integrally formed to extend from the rim portion  64  of the kinematic coupling groove  56  at the elongate straight sides. In one embodiment, the locking projection  68  includes a barb  72  and a tapered surface  74  on a distal end  76 . As illustrated in  FIGS. 3, 3A, and 3C , The rim portion at the half circular ends overlays the base plate  52  at an outwardly facing surface  77  and at the elongate straight sides the locking projections catch on an opposite inwardly facing surface  78  of a catch portion  79  of the base plate. 
         [0053]    Functionally, the continuous geometry of the kinematic coupling grooves component  56  provides the requisite strength to support the container portion  32  when coupled to fitting projections. The tapered surface  74  of the locking projection(s)  68  enables the kinematic coupling grooves component  56  to be slidingly inserted into the respective mounting apertures  62 . The barb  72  defined at the base of each tapered surface  74  is located to engage the respective mounting aperture  62  so that the locking projection  68  snaps into place to secure the kinematic coupling groove  56  to the base plate  52 . In one embodiment, the kinematic coupling grooves component  56  cannot be removed from the base plate  52  without first removing the base plate  52  from the container portion  32 . This helps prevent the kinematic coupling grooves component  56  from becoming dislodged from or tampered with the mounting apertures  62  inadvertently. 
         [0054]    Referring to  FIGS. 4A, 4B, 5G, and 5H , one of the wafer support components  50  of  FIGS. 1B and 1C  is depicted in isolation, along with a clip  82  designed to engage the wafer support component  50  for securing the wafer support component  50  to one of the side walls  41  of the shell  32 . The wafer support component  50  includes a front edge  86  and a back edge  88  with a plurality of wafer supports disposed therebetween. The back edge  88  includes a plurality of rear protrusions  90  that extend rearwardly. The rear protrusions  90  are configured to mate with the mounting pockets  46  on the back portion  42  of the container portion  32 . The front edge  86  includes a bracket that cooperates with the cooperating bracket  110  on the shell, the wafer support component bracket includes an array of front edge pockets  92   
         [0055]    The clip  82  includes a gripping portion  84  with a plurality of retention tabs  98 ,  100  extending rearwardly therefrom for maintaining the engagement of the wafer support shelf component to the shell and a plurality of locking tabs  101 , configured as detents, for securing the clip in place. The retention tabs  98 ,  100  are configured to mate with the front edge pockets  92  of the wafer support component  50 . In the depicted embodiment, some of the retention tabs  100  include a detent  102  proximate a free end  104 . 
         [0056]    Referring to  FIGS. 5A through 5C , the MAC  30  is depicted in various stages of assembly.  FIGS. 5D through 5H  depict the wafer support component configured as a shelf assembly  50  and further depict a locking insert or clip  82 . The depiction of  FIG. 5A  presents the container portion  32  with one of the wafer support assemblies  50  removed. Two of the brackets configured as mounting pockets  46  with receiving recesses  47  are visible in this view. The  FIG. 5A  also depicts a mounting bracket  110  that can be integrally formed on or otherwise attached to the side portion  40 , the mounting bracket  110  including a rearward edge  112  and defining a number of openings  113  that are adjacent to the side wall  41 . A further side bracket  114  integrally molded with the shell is also received by cooperating feature  115  configured as a slot in the wafer support component  50 . 
         [0057]    In assembly, the wafer support component  50  is positioned proximate one of the side portions  40  and cooperating brackets are engaged, specifically the rear protrusions  90  of the wafer support component  50  is inserted into the mounting pockets  46  of the back portion  42  of the container portion  32 , as depicted in  FIG. 5B . The front edge  86  of wafer support component  50  is rotated into position about a vertical axis in the y direction, whereby the front of the wafer support component is adjacent the side wall  41  immediately behind the mounting bracket  110 . With the wafer support component  50  so positioned, the clip  82  is inserted into the mounting bracket  110  so that the retention tabs  98 ,  100  extend through the mounting bracket  110  apertures  111  and into the front edge pockets  92  of the wafer support component  50 , as depicted in  FIG. 5C . When the locking clip  82  is fully inserted, the retention tabs  100  with the detents  102  snap into place so that the detents  102  engage the rearward edge  112  of the mounting bracket  110  or a rearward edge of the bracket of the wafer support shelves. The locking clip may be manually inserted and removed utilizing the handle portion  115 . 
         [0058]    In one embodiment, one of the mounting pockets  46  and/or rear protrusions  90  can be dimensioned for a close tolerance fit, while the remaining mounting pockets  46  and/or rear protrusions  90  are dimensioned for a looser fit. The close tolerance fit can provide registration for the wafer support component  50  relative to the back portion  42 , while the remaining, looser fitting mounting pockets  46  and rear protrusions  90  provide stability. For example, in the depicted embodiment, there are three mounting pockets  46  on the back portion  42  that mate with three rear protrusions  90  on the wafer support component  50 . The center mounting pocket  46  and rear protrusion  90  can be closely toleranced to provide a tight fit, while the upper and lower mounting pockets  46  and respective rear protrusions  90  are loose fitting. The loose fit of the upper and lower combinations still provide pitch, yaw and roll stability to prevent undue bending stress to be imparted on the central mounting pocket  46 /rear protrusion  90  combination. This arrangement provides for easier mounting of the wafer support component  50  into the plurality of mounting pockets  46  because only the close tolerance mounting pocket  46 /rear protrusion  90  combination needs to be carefully aligned. 
         [0059]    Referring to  FIGS. 6 through 6E, and 6H , a wafer retainer  120  is depicted in an embodiment of the invention. The wafer retainer  120  is mounted on the inside surface  121  of the door  44  utilizing conventional means such as bosses  122  extending from the door. The wafer retainer includes a substantially rectangular outer frame  124  having an upper member  126  and a lower member  128  separated by two opposing side members  130  generally defining a rectangular framework to be received by the inside wall surface of the door. At least one guide block  134  spans between the upper member  126  and the lower member  128 . A plurality of cantilevered fingers  138  extend from each of the side members in cantilevered fashion toward the guide block(s)  134 . The guide block comprise one or two vertical support members with a column of non cantilevered fixed wafer supports  135  each defining a seating position  136  for each of the forward edges of the wafers when the door is fully seated in the door frame. 
         [0060]    A slot  142  is defined between each pair of adjacent cantilevered fingers  138 , the slots  142  terminating at fixed end portions  144  of the cantilevered fingers  138 . Each cantilevered finger  138  is substantially flat and of substantially uniform thickness at the fixed end portions  144 . The cantilevered finger  138  takes on an angled shape at locations distal to the fixed end portions  144 , defining an angle or groove  143 . 
         [0061]    Functionally, the flatness of the fixed end portions  144  of the cantilevered fingers  138  is more conducive to bending than the angle-shaped portions of the cantilevered fingers  138  that are distal to the fixed end portions  144 . Accordingly, the fixed end portions  144  can act as a living hinge when a wafer or substrate engages the respective cantilevered finger  138 . The fixed end portions extend to and support an intermediate portion  145  and then the flexing distal end portion  146 . By this design, in one embodiment each cantilevered finger  138  generally flexes about a respective axis  148  that extends between the termination points, the distal tips  149  of the slots  142  on either side of the cantilevered finger  138 , while the finger itself remains comparatively rigid. 
         [0062]    In this way, the cantilevered fingers  138  can be shaped to substantially match the radius of the outer edge of the wafer or substrate that is being retained particularly when the door is seated. The angle surface defined on the cantilevered fingers  138  also aids in guiding and centering the wafers on the cantilevered fingers  138 . 
         [0063]    Each finger has the fixed or proximate end portion  144 , an intermediate portion  145 , and a distal flexing end portion  146  with a exposed wafer engaging surface  147  facing into the wafer container, that is away from the door. The finger initially extends horizontally from the vertical member and then at the intermediate portion  145  and end portion  146  extends slightly downward from the horizontal. The exposed wafer engaging surface has a linear recess defining the groove  143  or valley with the apex  150  of the groove defining the junction of an upper surface portion  151  and a lower surface portion  152  of the exposed wafer engaging surface. The groove or valley providing a wafer seating groove for when the door is fully seated in the door frame of the container portion. The wafer seating groove at the end portion of each finger is proximate the upper edge  154  or margin of the finger and extends to being approximately in the middle of the finger between the upper margin and lower margin  155  as the wafer seating groove approaches the fixed end portion, see  FIGS. 6F-6G  illustrating the progressive engagement of the wafer W as the cantileved finger is deflected from it original positions, shown in dashed lines, as indicated by the double arrows  156 . The lower surface portion of the exposed wafer engaging surface being wider, in the vertical direction, at the distal end portion of each finger and then narrowing toward the fixed end portion. 
         [0064]    As discussed above, the retainer further having one or two additional columns of fixed wafer seating portions in horizontal alignment with the wafer seating groove. 
         [0065]    As the door is inserted into the door frame of the container portion, front edges of the wafers will initially engage each finger, due to the sag of the wafers, at a lower point on the distal end portion of each finger. As the door is inserted further into the door frame the incline from vertical of each lower surface portion of each finger will urge the forward leading edge of each wafer upwardly, the horizontal extent of the engagement of each wafer with each finger will increase in horizontal width and extend closer to the fixed end portion of each finger as the door is further inserted until the door reaches its seated position. At such point, each wafer will be maximally engaged by the respective finger along most of the wafer engaging groove and will also be engaged by the additional column of fixed wafer seating portions. In an embodiment each wafer will be engaged by the door by two of the fingers and two additional fixed wafer seating portions. Thus, in an embodiment, there are two vertical columns of cantilevered wafer engaging fingers and two columns of fixed wafer seating portions. 
         [0066]    The downward tilt of the distal end portions of the cantilevered fingers is also illustrated in  FIG. 6H  where the wafer retainer is installed on the inside surface of a front door. 
         [0067]    Referring to  FIGS. 7A through 7C , one of the twist lock connectors  58  is depicted in an embodiment of the invention. A function of the twist lock connector is to secure the base plate  52  to the container not utilizing threads and using a partial rotation of less than 180 degrees. In another embodiment utilizing a rotation of about 90 degrees. Additionally the connectors may in embodiments provide an access port. The twist lock connector  58  of the depicted embodiment comprises a substantially cylindrical body  160  with a flanged end  162  and a flangeless end  164 , with a flange  166  of the flanged end  162  having a superior or outward-facing surface  170  and an inferior or inward-facing surface  172 . The cylindrical body  160  defines an interior through port  173 . The flange  166  can include holes or notches  176  at or near an outer perimeter  178  of the flange  166 . In one embodiment, the notches  176  are formed so that only a portion of the notch  176  is accessible from the outward-facing surface  170 , with the remainder of the notch  176  forming a recess  180  accessible from the inward-facing surface  172  ( FIG. 7C ). 
         [0068]    The twist lock connector  58  can also include an arcuate arm  184  formed proximate the flangeless end  164  of the cylindrical body  160 . The arcuate arm  184  defines a tangential slot  186  that is accessible from the flangeless end  164 . In one embodiment, a superior or outward tab  188  extends radially from the cylindrical body  160  and an inferior or inward tab  190  extends radially from the arcuate arm  184 , the tabs being located on opposing sides of the tangential slot  186 . The twist lock connector  58  can further include a boss  192  on the cylindrical body  160 . In the depicted embodiment, the boss  192  is substantially diametrically opposed to the tangential slot  186 . 
         [0069]    Referring to  FIG. 8 , a locking port  200  located on the base plate  52  is depicted in an embodiment of the invention. The locking port  200  is designed to selectively mate with the twist lock connector  58 . The locking port  200  can include opposing interior flanges  202 ,  204  on an interior perimeter  206  of the locking port  200 . In one embodiment, at least one of the interior flanges  202  defines a locking arm  208  that extends tangentially from the interior flange  202  in cantilevered fashion with a detent  209  located proximate the free end of the locking arm  208 . A protrusion  210  can also be located proximate the free end of the locking arm  208 . The interior flanges  202 ,  204  and protrusion  210  define a first gap  212  and a second gap  214 . 
         [0070]    Referring to  FIGS. 9A and 9B , male fastening members  213  are depicted in an embodiment of the invention. The male fastening member  213  can be configured as tubular boss  215  extends from the bottom of the container portion. In one embodiment of the invention, the boss  215  is integrally formed with the shell of the container portion, that is, unitary with the shell which may be configured as a purge or access port  216  of the container portion  32  is depicted in an embodiment of the invention. In other embodiments the fastening member may be a flanged member positioned in an hole through the shell  33 . In an embodiment, where the connector is associated with an access port, the boss has a passageway  219  that is in fluid communication with the interior of the container portion  32 . Any or all of the four connectors as illustrated may be associated with access ports. The access port  216  can be further characterized as having a base portion  220  and a free end  222 , and can include gussets  223  that extend from the lower portion  38  of the container along the base portion  220  of the fastening member  213 . In the depicted embodiment, the access port  216  also includes a secondary boss, protrusion, or pin  224  that extends radially outward from the body  218  proximate the free end  222 . 
         [0071]    Referring to  FIG. 9C , the coupling of the twist lock connector  58  to the access port  216  is depicted in an embodiment of the invention. (The base plate  52  has been removed from  FIGS. 9A through 9C  for clarity of the interaction between the twist lock connector  58  and the access port  216 . In operation, the base plate  52  would be included.) The protrusion  224  of the access port  216  cooperates with the tangential slot  186  of the twist lock connector  58  to provide a bayonet-style connection. In one embodiment, the flangeless end  164  of the twist lock connector  58  registers against the ends of the gussets  223 . 
         [0072]    Referring to  FIG. 9D , a purge valve  230  is depicted for use with embodiments of the invention. The purge valve  230  can comprise a grommet  232  having a passageway  234  that houses a check valve  236  for control of flow through the passageway  234 . The grommet  232  can also include exterior ribs  238  to facilitate sealing and friction fit of the grommet  232  within the access port  216  of the fastening member  213 . Any of a number of purge valves or grommets can be utilized within the access port  216 , such as, for example, found in U.S. Pat. No. 7,328,727 to Tieben et al., the disclosure of which is hereby incorporated by reference herein in its entirety except for express definitions contained therein. 
         [0073]    Referring to  FIGS. 10A and 10B , the twist lock connector  58  is depicted in operation. The twist lock connector  58  is oriented so that the boss  192  is aligned with the first gap  212  between the interior flanges  202 ,  204  of the locking port  200  and the outward and inward tabs  188 ,  190  are aligned with the second gap  214  ( FIG. 10A ). The twist lock connector  58  is then disposed in the locking port  200  so that the boss  192  and outward/inward tabs  188 ,  190  pass through the first and second gaps  212 ,  214  and the pin  224  of the access port  216  enters the tangential slot  186  of the twist lock connector. The inward-facing surface  172  of the flange  166  of the twist lock connector then contacts the interior flanges  202 ,  204  and protrusion  210  of the locking port  200 . 
         [0074]    At this point, the inward-facing surface  172  of the flange  166  of the twist lock connector also contacts the detent  209  on the distal end of the locking arm  208 , causing the locking arm  208  to bend away from inward-facing surface  172 . The twist lock connector  58  is then rotated ( FIG. 10B ) so that the pin  224  is positioned within tangential slot  186  between the outward and inward tabs  188 ,  190 . The rotation also aligns one of the recesses  180  on the inward-facing surface  172  of the flange  166  of the twist lock connector with the detent  209  at the distal end of the locking arm  208 . The resilience of the locking arm  208  causes the detent  209  to snap into the recess  180 . 
         [0075]    Functionally, the twist lock connector  58  captures the interior flanges  202 ,  204  of the base plate  52  between the inward-facing surface  172  of the flange  166  of the twist lock connector and the boss  192  and the outward tab  188  of the twist lock connector  58 . The tangential slot  186  and the pin  224  interact to secure the twist lock connector  58  against the ends of the gussets  223 , which determines the axial position of the twist lock connector relative to the access port  216 . 
         [0076]    The interaction between the arcuate arm  184  and the gusset  223  that it contacts provides stability to the connector, inhibiting the twist lock connector from canting on the access port  216 . The gusset  223  and pin  224  also secure the arcuate arm  184  in place to prevent the arcuate arm  184  from undergoing a bending moment under the load of the base plate. Instead, the transfer of forces to the arcuate arm  184  result primarily in a shear stress for improved strength. Also, the tangential dimension of the boss  192  and the inward tab  190  and the respective gaps  212 ,  214  that they pass through can be different to assure proper orientation of the twist lock connector  58  when locking the base plate  52  into place. 
         [0077]    The detent  209  at the distal end of the locking arm  208  prevents rotational movement of the twist lock connector  58  under normal operation. The protrusion  210  relieves the distal end of the locking arm  208  from the being over-extended and provides a more stable registration of the twist lock connector  58 . To remove the twist lock connector  58 , pins can be inserted into the portion of the notch  176  that is accessible from the outward-facing surface  170  of the flange  166  of the twist lock connector. The insertion depresses the locking arm  208  so that the detent  209  is freed from the recess  180 , and the twist lock connector  58  can be rotated out of position. 
         [0078]    The components of the wafer carrier described above may be conventially formed by injection molding polymers and assembly of the components.