Abstract:
A wafer container that reduces or alleviates one or more of the problems associated with excessive container wall deflection due to loading and excessive particulate generation, particularly as those problems are experienced with containers for 450 mm diameter and larger wafers. The container has an enclosure and door with interlocking features to enable transfer of tension load to the door to minimize deflection of container surfaces. The container may include a gasketing arrangement compatible with the interlock feature. The container may include a removable door guide that improves centering of the door during door installation, and that is made of low particle generating material to reduce particulates.

Description:
RELATED APPLICATIONS 
     The present application is a National Phase entry of PCT Application No. PCT/US2011/056944, filed Oct. 19, 2011, which claims priority to U.S. Provisional Patent Application No. 61/394,776, filed Oct. 20, 2010, U.S. Provisional Patent Application No. 61/421,309, filed Dec. 9, 2010, and U.S. Provisional Patent Application No. 61/523,218, filed Aug. 12, 2011, the disclosures of which are hereby incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to containers for sensitive substrates such as semiconductor wafers and in particular to the door and door frame interface of such containers. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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. 
     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. 
     A seal, generally in the form of a continuous loop of elastomeric material is fastened on the periphery of the door to provide sealing. Typically such seals are attached by inserting a base portion into a groove on the periphery of the door and/or securing the seal on pegs extending through holes in the seal. Often the “loop” of seal material is smaller than the circumference of the groove. This has proved to provide good seal retention on the rounded corners but the tension in the seal does little to retain the seal in the grooves in the large straight expanses of the top, bottom, and sides of the door. Uniformity and consistency of the sealing has been encountered particularly as the openings in wafer containers have increased to accommodate larger wafers. 
     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, as are door sealing issues due to uneven seals and distortion of the door to door-frame interface due to the deflection of container surfaces. 
     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. 
     There are several drawbacks associated with prior wafer handling devices or containers related to particulate generation. During the working life of a container, the closure or door is attached and removed many times by both robotic and manual means. With each attachment and removal, a portion of the door edge may scrape against the door frame of the container. This can result in the generation of loose particles which may become airborne to lodge on the wafers being contained. Equally important, doors of wafer handling devices or containers typically include cushions or channels which contact and support wafer edges. Optimally, such cushions or channels are designed to operate in concert with wafer receiving channels in the containers to securely retain a plurality of wafers. If a door is not, and cannot be accurately and repeatedly centered within a door frame, excessive contact and subsequent particle generation between the door cushions or channels and wafers may occur. 
     The problem of particle generation may also be attributed to the process by which doors and containers are manufactured. Containers and doors are usually formed by injection molding with plastic such as polycarbonate. Inherent in such molding is shrinkage and warpage of the molded parts. Although plastic injection molding techniques are highly advanced, there still may be individual deviations between different components form the same mold. While slight deviations do not generally compromise the function of a door in closing an container, they can change the working dimensions to the extent that contact (and the resultant particle generation) between a door and a door frame is increased. Dimensional changes can also be generated by the dies themselves, as a result of normal wear and tear. This problem is accentuated when the tolerances of the components of doors and containers are stacked or added. 
     Yet another drawback occurs because these wafer carriers are robotically opened and closed. The carriers will be opened by multiple pieces of equipment which may each be set up differently. Also such equipment may go out of adjustment and is subject to wear and tear. Such equipment may not then be perfectly aligned resulting in undesirable and/or excessive door-frame contact and a situation of excessive abrasion and/or particle generation. 
     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 
     Embodiments of the invention address the need of the industry for a wafer container that reduces or alleviates one or more of the problems associated with excessive container wall deflection due to loading and excessive particulate generation, particularly as those problems are experienced with containers for 450 mm diameter and larger wafers. 
     In an embodiment, a front opening wafer container suitable for large diameter wafers uses an elastomeric gasket configured and shaped as a rectangular frame with rounded corners. The elastomeric material may be sandwiched between a gasket retention frame and a door housing member. In an embodiment of the invention, the gasket retention frame covers a substantial portion of the inside face of the door. In an embodiment of the invention, the gasket retention frame has a door guide member that extends around the periphery of the door and cooperates with a similar structure on the door frame to provide a guiding action if the door is not perfectly aligned when it is inserted into the door frame, and thereby inhibiting particulate generation by frictional contact between components. The door guide member and cooperating door frame portion may each have tapered surfaces that cooperate and engage each other. 
     In an embodiment of the invention the gasket material is configured as sheet material having a relatively uniform thickness. An exposed tip of the seal extends outwardly to engage a side wall of the door frame of the enclosure portion. In other embodiments, the gasket is not of relatively uniform thickness with the gasket material molded. In an embodiment of the invention, the gasket retention framework can be integrally formed with wafer cushions. In another embodiment, the gasket material is overmolded on the gasket retention frame. 
     In an embodiment, the inside surface of the front door intermediate the wafer cushions and the seal is provided by a single unitary frame that overlies the gasket layer, with the peripheral edge of the gasket material protruding radially outward from the door for engaging the inwardly facing surface of the door frame. 
     In an embodiment of the invention, in a door for a front opening wafer container, the periphery of the door has three distinct layers exposed at the periphery: a door base portion, an elastomeric seal, and a gasket frame. 
     In an embodiment of the invention, the sealing member provides an interlocking portion that is inserted into a circumferential groove extending around the door opening. The sealing member has a body portion with a retained portion secured to the door and an outwardly extending portion extending from the retained portion. The outwardly extending portion may be L-shaped and include a radially extending portion and an axially extending portion with the axially extending portion defining the interlocking portion. The sealing member may be endless, that is, loop shaped. The sealing member can have door frame elongation resistance features that can secure the door frame, particularly the midportion top and midportion bottom of the door frame, such that the door in association with the sealing member inhibits vertical elongation of the door frame when the container is supported by the top of the container portion, for example by a robotic flange attached thereto and particularly when the container is loaded with wafers. Specific aspects of embodiments may include the sealing member being under circumferential tension which may increase the effective durometer of the sealing member and enhance the resistance of the radially extending portion to resist radial expansion of the outwardly extending portion. Such radial expansion may occur by the axially extending portion rotating upwardly and in a direction away from the container portion. A rigid stop may be positioned opposite the container portion side of the extending portion to preclude or reduce said rotation. A angled strip of material of a non elastomeric quality or of a lesser elastomeric characteristic that the body portion of the elastomeric seal, can be utilized to further assist the axially extending portion in resisting the rotation upward and away from the container portion caused by elongation stresses in the door frame. 
     In an embodiment, the gasket retention framework also forms a peripheral door guide and frame shape retainer with a projection projecting in the “z” direction and extending around the periphery of the door with a taper on the inside surface of the projection. The peripheral door guide is configured to engage a corresponding generally v-shaped recess with a matching tapered surface on the door frame. 
     In an embodiment, a semiconductor wafer carrier has an enclosure with a door frame defining an opening for insertion and removal of wafers, a door for closing and sealing said opening, and separately formed door guides for controlling the interface between said door and the enclosure. In some embodiments, the door guides each comprise elongate members that extend along the perimeter of the door, and are centrally positioned on one, two or four perimeter side surfaces of the doors. Each provide locating, that is positioning functions in both the “x” and “y” directions (the “z” direction being the insertion and removal direction of the door into and out of the door frame). 
     In an embodiment, the door guides have a peripherally extending elongate and thin rib that fits into a slot in the door frame. Each door guide may have a U-shaped opening with the legs of the U slanted to provide a guide in positioning the edge, with the U facing inward in the “z” direction towards the enclosure and enclosure door frame before and when the door is inserted into the door frame. The rib fitting into the slot may be seated, that is, in contact and engagement with the door frame or may be separated and not in direct contact with the door frame. In a preferred embodiment, the door has a vertical and a horizontal centerline and a door guide is positioned on the top peripheral side centered about the door centerline. A door guide may similarly be positioned on the lateral peripheral sides and the bottom peripheral side, each centered about the respective door centerline. Each door guide may have two positioning portions with each providing guide surfaces for positioning the door in the x and y directions. 
     In an embodiment, each door guide may have a detent, for example a tongue shaped detent, that engages a slot in the door frame. Each door guide may have two detents. Further, each door guide may have receivers for engaging projections on the door frame or vice versa. The projections and receivers can be wedge shaped to provide a definitive and guided-in locking position. Thus, in embodiments the guide extends along the peripheral edge of the door and is attached without separate fasteners. 
     In an embodiment, the guides are formed from a mixture including polybutylene terephthalate (PBT) or Acetal. These materials seem to have a favorable low particle generating characteristics in this context, that is minimizing particle generation during door-edge to door-frame engagement. 
     In alternative embodiments, the guides may be attached to the door frames in addition to or rather than the doors. Where the guides are attached to both the door and door frame, the guides may be attached in an offset or face to face cooperating relation. 
     The guides may be utilized with or without corner guides such as disclosed in U.S. Pat. Nos. 6,206,196 and 6,464,081, both fully incorporated herein by reference. 
     According to an embodiment, a front opening container for semiconductor wafers includes an enclosure portion including a top wall, a bottom wall, a pair of side walls, a back wall, and a door frame opposite the back wall, the door frame defining a front opening, the door frame having a plurality of intersecting side walls forming a plurality of door frame corners, each side wall defining a ramped portion intermediate adjacent door frame corners, and a door removably received in the door frame for closing the front opening, the door comprising a body portion presenting a plurality of intersecting peripheral faces. The container further includes a plurality of door guides, each door guide disposed on a separate one of the peripheral faces such that each door guide is engaged with a separate one of the ramped portions of the door frame when the door is received in the door frame. 
     According to an embodiment, the door frame may define an outwardly facing recess inward from each ramped portion and extending parallel with a front edge of the front opening. Each door guide may define an edge, the edge of the door guide being engaged in the recess to interlock the door with the enclosure portion when the door is received in the door frame. The recess may be generally v-shaped and present an engagement surface, and the edge of the door guide may have an engagement surface conformingly disposed so as to confront the engagement surface of the recess when the edge of the door guide is received in the recess. 
     In an embodiment, each of the plurality of peripheral faces of the body portion defines a door guide recess, and a separate one of the door guides is received in each of the door guide recesses. Each of the door guides may have at least one engagement structure, the at least one engagement structure received by a corresponding engagement structure in the door guide recess. The at least one engagement structure can be an engagement tab, and the corresponding engagement structure can be an aperture. 
     In an embodiment, the door of the container may include an elastomeric seal extending around a periphery of the door, the elastomeric seal engaging structure on the door frame when the door is received in the door frame to hermetically seal the enclosure portion. The container may also include a wafer cushion disposed on a rear side of the door. The door guide can be made from a low particle generating material, which can be acetal or PBT. 
     In another embodiment, a front opening container for semiconductor wafers includes an enclosure portion including a top wall, a bottom wall, a pair of side walls, a back wall, and a door frame opposite the back wall. The door frame defines a front opening and a forwardly facing recess extending around an inner periphery of the door frame parallel with a front edge of the door frame. A door is removably received in the door frame for closing the front opening. The door includes a body portion presenting a rear side and a gasket assembly disposed on the rear side. The gasket assembly includes a gasket frame and a gasket. The gasket frame defines an elongate projection extending around a periphery of the door, the gasket being retained between the gasket frame and the body portion. The gasket includes a laterally projecting sealing portion. The projection of the gasket frame is received in the recess of the door frame to interlock the door with the door frame when the door is received in the door frame, and the laterally projecting portion of the gasket engages and seals against a side wall of the door frame when the door is received in the door frame. In an embodiment, the gasket assembly includes an integrally formed wafer cushion. In some embodiments, the gasket assembly substantially covers the entire rear side of the body portion of the door. In a further embodiment, the gasket can be over-molded on the gasket frame. 
     In an embodiment, the forwardly facing recess is generally v-shaped and presents an engagement surface, and the projection of the gasket assembly has an engagement surface conformingly disposed so as to confront the engagement surface of the recess when the projection is received in the recess. 
     In a further embodiment, a front opening container for semiconductor wafers includes an enclosure portion including a top wall, a bottom wall, a pair of side walls, a back wall, and a rectangular door frame opposite the back wall, the door frame defining a front opening, the door frame defined by side walls extending between corners of the rectangular door frame, each side wall defining a ramped portion intermediate adjacent corners. A rectangular door is removably received in the door frame for closing the front opening, the door comprising a body portion presenting four intersecting peripheral faces. The container further includes a plurality of door guides, each door guide disposed on a separate one of the peripheral faces such that each door guide is engaged with a separate one of the ramped portions of the door frame when the door is received in the door frame. 
     In an embodiment, the door frame defines an outwardly facing recess inward from each ramped portion and extending parallel with a front edge of the front opening. Each door guide defines an engagement structure, the engagement structure of the door guide being engaged in the recess to interlock the door with the enclosure portion when the door is received in the door frame. In some embodiments, the recess is generally v-shaped and presents an engagement surface, and the engagement structure of the door guide has an engagement surface conformingly disposed so as to confront the engagement surface of the recess when the engagement structure of the door guide is received in the recess. In some further embodiments, each of the plurality of peripheral faces of the body portion defines a door guide recess, and a separate one of the door guides is received in each of the door guide recesses. Each of the door guides may have at least one engagement structure, the at least one engagement structure received by a corresponding engagement structure in the door guide recess. 
     An advantage and feature of the invention is that a shock absorption characteristic is provided by having the door frame engaging portion of the door having a gasket layer between it and the door base. This reduces the transfer of shock waves, such as from the operation of the latch mechanisms, into the container portion, such shock waves, can then launch particles from the inside surfaces of the container portion. 
     An advantage and feature of the invention is that a the gasket engages with a sealing surface substantially extending in the z-x plane or the z-y plane. The gasket lip extending from the door periphery extends outward to engage substantially normally with sealing surface. The effect of slight distortions in the door frame on affecting the sealing integrity is minimized. 
     An advantage and feature of embodiments of the invention is a circumferential seal comprising an elastomeric body member and a rigidizing strip member extending therearound and adhered thereto. The rigidizing strip member is of a different durometer hardness. 
     An advantage and feature of embodiments of the invention is a circumferential seal in a loop shape and comprising an elastomeric body member and a strip member extending around the length of the loop. The strip member may provide an engagement surface. 
     An advantage and feature of embodiments of the present invention to provide the door of a wafer container with removable door guides centered on a peripheral face of the door. 
     An advantage and feature of embodiments of the present invention is to reduce the amount of particulates generated by frictional contact between a door and a door frame. 
     An advantage and feature of embodiments of the present invention is to facilitate centering of a door within a door frame. 
     An advantage and feature of embodiments of the present invention is to reduce the amount of particulates generated by frictional contact between door mounted cushions and semiconductor wafer edges. 
     An advantage and feature of embodiments of the present invention is to increase permissible tolerances between a door and a door frame. 
     An advantage and feature of embodiments of the present invention is that guides may be removably attached at various locations on a door. 
     An advantage and feature of embodiments of the invention is that the guides are fabricated out of a relatively hard and low friction material which resists wear. 
     An advantage and feature of embodiments of the invention is to reduce deflection of the top, bottom, sides, and/or front of a container enclosure by interlocking the door of the container with the enclosure portion. 
     An advantage and feature of embodiments of the invention is to reduce the velocity of air entering the container when the door is removed from the enclosure portion, thereby inhibiting the spread of particulates to the inside of the enclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the present invention may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
         FIG. 1  is an exploded front isometric view of a front-opening wafer container according to an embodiment of the invention; 
         FIG. 2  is an exploded isometric view of an embodiment of a front door assembly for the container of  FIG. 1 ; 
         FIG. 3  is an exploded isometric view of another embodiment of a front door assembly for the container of  FIG. 1 ; 
         FIG. 4  is a fragmentary cross-sectional view of the container of  FIG. 1 , depicting the front door assembly engaged in the door frame of the enclosure portion; 
         FIG. 4A  is a fragmentary cross-sectional view of the container of  FIG. 4  with door slightly separated from the door frame of the enclosure position; 
         FIG. 5  is an exploded view of a front door assembly, depicting the wafer cushion assembly registered for placement on the door body; 
         FIG. 6  is an isometric view of a front door cushion assembly with the cushion material extending across substantially the entirety of the inside facing surface of the door; 
         FIG. 7  is an isometric view of the rear side of the front door cushion assembly of  FIG. 6 ; 
         FIG. 8  is a cross-sectional view taken through a corner of a container portion and front door assembly with the front door assembly in a first stage of insertion in the door frame; 
         FIG. 9  a cross-sectional view of the corner of the container portion and front door assembly depicted in  FIG. 8 , with the front door assembly in a second stage of insertion in the door frame; 
         FIG. 10  a cross-sectional view of the corner of the container portion and front door assembly depicted in  FIG. 8 , with the front door assembly fully seated in the door frame; 
         FIG. 11  is a fragmentary cross-sectional view taken at section  11 - 11  of  FIG. 1 ; 
         FIG. 12  is a fragmentary cross-sectional view of a door engaged with a door frame of a container portion according to an alternative embodiment of the invention; 
         FIG. 13  is an exploded front isometric view of a front-opening wafer container according to another embodiment of the invention; 
         FIG. 14  is an assembled front isometric view of the front-opening wafer container of  FIG. 13 ; 
         FIG. 15  is an isometric view of the bottom edge of the door frame of the container of  FIG. 13 , depicting the ramped door guide engagement portions and interlocking feature; 
         FIG. 16  is an isometric view of the rear side of the door assembly of the wafer container of  FIG. 13 ; 
         FIG. 17  is a detail view of one of the side door guides of the door assembly of  FIG. 16 ; 
         FIG. 18  is a detail view of the top door guide of the door of  FIG. 16 ; 
         FIG. 19  is a partial cross-sectional view through the bottom door guide taken at section  19 - 19  of  FIG. 14 ; 
         FIG. 19A  is a partial cross-sectional view same as  FIG. 19  only showing the enclosed portion. 
         FIG. 20  is an isometric view of the rear side of the door of  FIG. 16 , with the door guides omitted to show the door guide engaging apertures; 
         FIG. 21  is a partial isometric view of the side of the door of  FIG. 16 , depicting the door guide in a position registered for insertion in the receiving recess; 
         FIG. 22  is an isometric view of the inner side of a door guide of the door assembly of  FIG. 16 ; and 
         FIG. 23  is an isometric view of the outer side of the door guide of  FIG. 22 . 
     
    
    
     While the present invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the present invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention. 
     DETAILED DESCRIPTION 
     For purposes of this application, relative direction may be described in terms of “x” and “y” and “z” directions, and these designations relative to the parts of the container are intended to be in accordance with the directional key provided as a part of  FIGS. 1, 13 and 14 . 
     Referring now to  FIG. 1 , a front opening wafer container  20  generally includes an enclosure portion  22  and a front door  24 . Enclosure portion  22  generally includes top wall  26 , bottom wall  27 , side walls  28 ,  30 , back wall  32 , and door frame  34  defining a front opening  36 . In addition, latch bolt recesses  56  are defined in each of top side  42  and bottom side  46  of door frame  34 . Each latch bolt recess  56  is surrounded by raised portion  58 . Outwardly facing interlock groove  55  is defined at inner edge  57  of door frame  34 . Wafer support structure  60  may be provided inside enclosure portion  22  for receiving wafers in a plurality of slots  62 . A robotic lifting flange  64  and a kinematic coupling  66  as are known in the art may be provided on the top and bottom outer surfaces respectively of enclosure portion  22 . 
     Front door  24  generally includes body portion  68  presenting rear side  70 , front side  72 , top peripheral face  74 , side peripheral faces  76 ,  78 , and bottom peripheral face  80 . A pair of latch recesses (not depicted) are defined in front side  72 , and are covered by front panel  82 . Each latch recess receives a latching mechanism (not depicted), operable by a key insertable though key apertures  84  in front panel  82  to selectively extend and retract latch bolts  86  to engage in latch bolt recesses  56  of container portion  22  to secure front door  24  in door frame  34 . The latch mechanisms can be generally configured as disclosed in U.S. Pat. No. 4,995,430; 7,182,203; or 7,168,587, all of which are owned by the owner of the instant application, and all of which are hereby incorporated herein by reference. 
     In an embodiment depicted in  FIG. 2 , front door  24  includes wafer cushion member  87  having wafer cushion  88  with a plurality of wafer engaging portions  90 . Wafer cushion member  87  is positioned on rear side  70  of body portion  68  with gasket member  92  interposed between the two. Notably, wafer cushion member  87  covers substantially the entirety of rear side  70  in the depicted embodiment. Wafer cushion  88  is received in recess  92  formed in body portion  68 , with recess  92  extending from the top of the door to the bottom of the door and is centrally positioned with respect to the left and right sides of the door. The recess has different depths, with the deepest portion extending along the vertical mid-line of recess  92 . Wafer cushion member  87  defines forwardly projecting lip  89  around its entire periphery. 
     Referring to  FIG. 3 , an alternative embodiment of front door  24  is depicted. Gasket frame assembly  94  generally includes gasket frame  96 , and gasket  98 . Gasket  98  can be either separately formed from gasket frame  96  as depicted, or over-molded on gasket frame  96  using commonly known over-molding techniques. Gasket frame  96  defines forwardly projecting lip  97  around its entire periphery. Wafer cushion member  100  is separate from gasket frame assembly  94  and includes wafer cushion  88  with a plurality of wafer engaging portions  90 . Wafer cushion member  100  is sandwiched between gasket frame assembly  94  and body portion  68 . Again, wafer cushion  88  is received in recess  92  formed in body portion  68 . 
       FIG. 4  depicts, in fragmentary cross-section, front door  24  fully engaged in door frame  34 .  FIG. 4A  shows it partially separated. Forwardly projecting lip  89  of wafer cushion member  87  is received in generally v-shaped interlock groove  55  of door frame  34 , with sloped engagement surface  89   a  of lip  89  abutting sloped engagement surface  55   a  of interlock groove  55 . Gasket member  92 , which is sandwiched between wafer cushion member  87  and body portion  68 , has projecting portion  202 , which includes laterally projecting lip  204 . Lip  204  engages and seals with side wall  205  of door frame  34 . It will be appreciated that inwardly facing surface  206  of wafer cushion member  87  can be angled at a slightly different angle from outwardly facing surface  208  of body portion  68  to compress gasket member  92  and provide a clamping force in order to better secure gasket member  92  in place and prevent any slippage or dislocation of gasket member  92 . 
     It will be appreciated that that the abutting engagement of sloped surface  55   a  and sloped surface  89   a  forms an interlock between front door  24  and container portion  22 , tending to resist outward deflection of top wall  26 , bottom wall  27 , side walls  28 ,  30 , door frame  34 , and front door  24 . For example, when container  20  is loaded with wafers and lifted with robotic lifting flange  64 , the weight of the wafers will apply a force tending to deflect top wall  26  and bottom wall  27  away from each other, especially at front opening  36 . With front door  24  engaged in door frame  34  as depicted in  FIG. 4 , the engagement of forwardly projecting lip  89  of wafer cushion member  87  in interlock groove  55  enables door  24  to be loaded in tension, thereby resisting deflection of top wall  26  and bottom wall  27 . 
       FIGS. 8-10  depict front door  24  in successive stages of engagement in door frame  34 . In  FIG. 8 , front door  24  is registered with door frame  34  with projecting portion  202  of gasket member  92  inside outer edge  54  of door frame  34 . As front door  24  is advanced into door frame  34  as depicted in  FIG. 9 , the leading edges of wafers  210  engage lower sloped surfaces  212  of wafer engaging portions  90 , causing wafers to ride upward. Projecting portion  202  begins to engage with side wall  205  of door frame  34 . In  FIG. 10 , as front door  24  is advanced into full engagement in door frame  34 , the edges of wafers  210  seat in the v-shaped wafer engaging portions  90 . Forwardly projecting lip  89  of wafer cushion member  87  is received in interlock groove  55 , with sloped surface  89   a  of lip  89  abutting sloped surface  55   a  of interlock groove  55 . Lip  204  engages and seals against side wall  205  of door frame  34 , thereby sealing the interior of enclosure portion  22  and wafers  210  from outside contaminants. 
     As depicted in  FIGS. 5-7 , wafer cushion member  87  can be secured to rear side  70  of body portion  68  with a plurality of engagement structures  214  disposed on rear side  70  proximate each of side peripheral faces  76 ,  78 , that engage corresponding hooks  216  on wafer cushion member  87 . If desired, additional engagement structures  218  can be provided nearer the lateral midpoint of rear side  70 , engagable with correspondingly disposed hooks on wafer cushion member  87 , to further secure wafer cushion member  87  in place. 
     Another advantageous aspect of wafer cushion member  87  in certain embodiments of the invention is depicted in  FIGS. 2 and 11 . Each wafer engaging portion  90  of wafer cushion  88  is resilient and serves as a spring, when the wafers are fully engaged, to apply limited force to each wafer so as to hold the wafers in place and cushion the wafers against physical shock. According to the depicted embodiment, each wafer engaging portion  90  has a ramped protrusion  220  proximate the outboard edge. This ramped protrusion  220  is disposed proximate the latch mechanisms  222  of front door  24  when wafer cushion member  87  is disposed on body portion  68 . The top side of ramped protrusion  220  is the first point of contact for wafers  210  as front door  24  is advanced into door frame  34 . As more force is applied by each wafer  210  to wafer engaging portion  90 , the wafer engaging portions  90  deflect. Since initial contact occurs at ramped protrusions  220 , more of the cushion loading due to the force applied by the spring action of wafer engaging portions  90  is applied to body portion  68  along latching mechanisms  222 , where front door  24  is more able to resist outward deflection due to the engagement of latch bolts  86  in latch bolt recesses  56 . Consequently, distortion of container  20  from the cushion loading is relatively minimized. It will be appreciated that, in other embodiments, the first point of initial contact of wafers  210  with the bottom edge of ramped protrusion  220  to achieve the same effect. 
     Another advantageous aspect of certain embodiments is provided by the raised portions  58  around each of the latch bolt recesses  56 . These raised portions  58 , coupled with the slight outward slope of side wall  205  of door frame  34 , enable front door  24  to be spaced apart from door frame  34 , especially at outer edge  35 . In use, when front door  24  is removed and replaced in door frame  34 , there may be movement of air inwardly into enclosure portion  22  due to the hermitic seal. The larger clearance provided by spacing front door  24  further away from door frame  34  may cause the velocity of the air to be reduced from what it would otherwise be, thereby reducing the likelihood that particulates will be entrained in the air and carried into enclosure portion  22  to contaminate the wafers inside. Further, the raised portions  58  can minimize the clearance between front door  24  and door frame  34  at the latch locations, thereby minimizing the unsupported length of latch bolts  86  when they are engaged in latch bolt recesses  56 , and reducing possible distortion of front door  24  in the “z” direction. 
     Referring to  FIG. 12 , an alternative embodiment is depicted that has front door  102  engaged in door frame  104  of container portion  106 . Latch members  108  extend and retract into receivers  109  on door frame  104  to removably secure the door in the door frame. Sealing member  110  or gasket has elastomeric body  113  with retained portion  111  that is retained by being sandwiched between frame or base portion  117  of the door and inner retention frame  120 . Elastomeric body  113  also has non-retained and outwardly extending portion  112 . Outwardly extending portion  112  has radially extending portion  116  and axially extending portion  114 . Positioned on the container portion side of the seal is strip portion  130  formed of a different material, preferably a polymeric material, that may be non-elastomeric and extends, in a radial perspective, outwardly from the inner retention frame, where it may be adhered thereto, onto the inwardly facing (toward the container portion) vertical face  136  of elastomeric gasket  110 , and then angles inwardly and is adhered to angled inward face  140  of the elastomeric gasket for insertion in recess  144 . The strip portion may form a door frame engagement portion to primarily or exclusively contact the door rather than the elastomeric body portion. The door frame engagement strip portion  130  extends circumferentially around the inside perimeter of the door frame and engages with the outwardly extending angled protrusion  148  of door frame  104 . As depicted, the strip portion may conform to the shape of the door frame where it engages. The elastomeric body and the door frame engagement strip portion define sealing portion  150 . The door frame engagement strip portion may be formed from a rigid and resilient strip of polymer material and preferably extends endlessly around the door and is adhered to the elastomeric gasket material such as by over-molding. The engagement strip portion can form the entirety of the engagement of the sealing portion with the door or a portion of the elastomeric gasket can also directly contact and seal with the door. The engagement strip portion can thus provide a sealing engagement that adheres less to the door frame providing for easier removal of the door as compared to the elastomeric gasket material. 
       FIG. 12  also illustrates a further embodiment of the securement of the gasket  111  between the inner retention frame  120  and base portion  117  of the door. The frame  120  clamps on to an inwardly extending (towards the container portion) protrusion  160  of the door base portion  117  with sealing member  110  also sandwiched between the frame and protrusion at recess  164  in frame  120 , and also being compressed therein. Although only a cross section is illustrated at the top of the door, the interfacing components and features, such as the sealing member, strip portion, protrusion, recess, preferably extend the around the entirety of the outer periphery of the door and inner periphery of the door frame. 
     It will be appreciated that any or all of the components of wafer container  20  may generally be injection molded from polymers typically used for semiconductor wafers. Such materials include, but are not limited to, polycarbonates, fluoropolymers, and polyetheretherketone. 
     A wafer container  300  according to another embodiment of the present invention is depicted in  FIGS. 13-23 , and generally includes enclosure portion  302  and door  304 . Enclosure portion  322 , as depicted in  FIGS. 13 and 14  generally includes bottom wall  306 , top wall  308 , side walls  310 ,  312 , back wall  314 , and door frame  316  on the front side of the enclosure defining an opening  318  for receiving door  304 . Ramped portions  320  are defined on the inner periphery of door frame  316  proximate the mid-point of each side  322 ,  324 ,  326 ,  328 , of the door frame  316 , each sloping toward the outer edge  330  in the “z” axis direction as annotated in  FIG. 13 . Adjacent and inwardly from each ramped portion  320 , an elongate projection  332  extends outwardly in the “z” axis direction, defining a generally v-shaped recess  334  extending parallel to outer edge  330  of door frame  316 . In addition, latch bolt recesses  336  are defined in each of bottom side  322  and top side  328  of door frame  316 . Each latch bolt recess  336  is surrounded by a raised portion  338 . A wafer support structure (not depicted) may be provided inside enclosure portion  302  for receiving wafers (not depicted) in a plurality of slots defined in the structure. A robotic lifting flange  340  and a kinematic coupling  342  are known in the art may be provided on the top and bottom outer surfaces respectively of enclosure  302 . 
     Door  304  as depicted in  FIGS. 13-23  generally includes body portion  344  presenting rear side  346 , front side  348 , top peripheral face  350 , side peripheral faces  352 ,  354 , and bottom peripheral face  356 . A pair of latch recesses (not depicted) are defined in front side  348 , and are covered by front panel  358 . Each latch recess receives a latching mechanism (not depicted), operable by a key insertable though key apertures  360  in front panel  358  to selectively extend and retract latch bolts  361 . Wafer cushion  500  is disposed on rear side  346 . 
     According to an embodiment of the invention, each of top peripheral face  350 , side peripheral faces  352 ,  354 , and bottom peripheral face  356  defines a door guide recess  362 . The recesses  362  in top peripheral face  350  and bottom peripheral face  356  are centered on vertical door centerline  364 , while recesses  362  in the side peripheral faces  352 ,  354 , are centered on horizontal door centerline  366 . 
     Each door guide recess  362  is defined by inner wall  368 , side walls  370 ,  372 , and bottom wall  374  as depicted in  FIG. 20 . Groove  376  is defined in each of side walls  370 ,  372 , and bottom wall  374 , and extends around the periphery of the recess  362 . Bottom wall  374  also defines guide engagement apertures  378 ,  380 , and central guide engagement aperture  379 . A pair of guide tabs  382  extend outwardly from inner wall  368  proximate each end of the recess  362 . 
     Body portion  344  may also define corner door guide receiving recesses  384  at each of the corners  386 ,  388 ,  390 ,  392 , of door  304 . Each recess  384  can receive a corner door guide (not depicted) as is known in the art to assist in locating door  304  in door frame  316 . 
     Door guide  394  is depicted in Figures and generally includes a unitary elongate body portion  396  formed from polymer material having a low coefficient of friction and favorable low particle generating characteristics, such as mixture of PBT or Acetal. Tabs  398  extend laterally outward from each end  400 ,  402 . Ribs  404  are provided on bottom edge  406 , and the central rib  404  includes central locating tab  408 . Engagement tabs  410  extend downwardly proximate each end  400 ,  402 , and include detent  412 . Inner side  414  also has a wedge shaped projection  416  defined proximate each end  400 ,  402 , each projection  416  defining groove  418 . Top edge  420  is defined in a generally U-shaped opening between legs  422 ,  424 . The sides  426  of the U-shaped opening may be slightly inclined as depicted. 
     One of door guides  394  is removably received in each of door guide recesses  362  in top peripheral face  350 , side peripheral faces  352 ,  354 , and bottom peripheral face  356 , of body portion  344 . Door guide  394  is inserted by registering each of grooves  418  with one of guide tabs  382  and advancing the door guide downwardly as depicted in  FIG. 21 . As guide  394  is advanced downward, tabs  398  are received and slide in the groove  376  defined in each of side walls  370 ,  372 . Once guide  394  is fully inserted, ribs  404  are received in groove  376  in bottom wall  374  with central locating tab  408  extending through central guide engagement aperture  379 . Engagement tabs  410  are received through guide engagement apertures  378 ,  380 , and detent  412  engages behind bottom wall  374  to secure guide  394  in position. With guide  394  in position, guide surfaces  428  face outwardly. 
     Door  304  is engaged in door frame  316  of enclosure portion  302  by registering door  304  with the opening defined by door frame  316  as depicted in  FIG. 13 . As door  304  is advanced into frame  316 , guide surfaces  428  of door guides  394 , engage and slide on ramped portions  320  on the inner periphery of door frame  316 . The slight slope of ramped portions  320  helps guide door  304  into the desired position. Moreover, the inclined edges  426  of the U-shaped opening defining top edge  420  may also assist in locating and centering door  304  in door frame  316  in the “x” and “y” directions. Once door  304  is fully engaged in frame  316 , the latch mechanisms can be actuated to move latch bolts  361  into latch bolt recesses  336  to secure door  304  in place. 
     As depicted in the cross-sectional view of  FIG. 19 , with door  304  in the fully engaged position in frame  316 , top edge  420  of guide  394  engages in recess  334 . Top edge  420  may be seated in recess  334 , that is in contact and engagement, or may be separated and not in direct contact. Elastomeric gasket  430 , received in recess  431  on door  304 , engages with shoulder  432  on door frame  316  to provide hermetic sealing of the container. The engagement of top edge  420  of guide  394  in recess  334 , may serve to “interlock” door  304  in frame  316 , to inhibit unintended disengagement of door  304 , and damage to the integrity of the hermetic seal occurring due to mechanical shocks to the container. Further, it will be appreciated that the abutting engagement of sloped engagement surface  434  on top edge  420  of door guide  394  with sloped engagement surface  436  in recess  334  may form an interlock between door  304  and container portion  302 , tending to resist outward deflection of top wall  308 , side walls  310 ,  312 , bottom wall  306 , door frame  316 , and door  304 . For example, when container  300  is loaded with wafers and lifted with robotic lifting flange  340 , the weight of the wafers will apply a force tending to deflect top wall  308  and bottom wall  306  away from each other, especially at front opening  318 . With door  304  engaged in door frame  316  as depicted in  FIG. 19 , the engagement of forwardly projecting top edge  420  of door guide  394  in recess  334  enables door  304  to be loaded in tension, thereby resisting deflection of top wall  308  and bottom wall  306 . 
     Still further, it is believed that the central positioning of door guides  394  on top peripheral face  350  and bottom peripheral face  356  on vertical door centerline  364 , the central positioning of door guides  394  on the side peripheral faces  352 ,  354 , on horizontal door centerline  366  serve to better locate and position door  304  in the “x”, “y” and “z” directions than previously known corner door guides alone. It will be appreciated that the door guides  394  according to embodiments of the present invention may be used alone without corner guides or in conjunction with corner guides if desired to give additional positioning accuracy. 
     Another advantageous aspect of certain embodiments is provided by the raised portions  338  around each of the latch bolt recesses  336 . These raised portions  338 , coupled with the slight outward slope of side wall  490  of door frame  316  around its entire periphery, enable door  304  to be spaced apart from door frame  316 , especially at outer edge  330 . In use, when door  304  is removed and replaced in door frame  316 , there may be movement of air inwardly into enclosure portion  302  due to the hermetic seal. The larger clearance provided by spacing door  304  further away from door frame  316  may cause the velocity of the air to be reduced from what it would otherwise be, thereby reducing the likelihood that particulates will be entrained in the air and carried into enclosure portion  302  to contaminate the wafers inside. Further, the raised portions  338  can minimize the clearance between door  304  and door frame  316  at the latch locations, thereby minimizing the unsupported length of latch bolts  361  when they are engaged in latch bolt recesses  336 , and reducing possible distortion of door  304  in the “z” direction. 
     The foregoing descriptions present numerous specific details that provide a thorough understanding of various embodiments of the invention. It will be apparent to one skilled in the art that various embodiments, having been disclosed herein, may be practiced without some or all of these specific details. In other instances, components as are known to those of ordinary skill in the art have not been described in detail herein in order to avoid unnecessarily obscuring the present invention. It is to be understood that even though numerous characteristics and advantages of various embodiments are set forth in the foregoing description, together with details of the structure and function of various embodiments, this disclosure is illustrative only. Other embodiments may be constructed that nevertheless employ the principles and spirit of the present invention. Accordingly, this application is intended to cover any adaptations or variations of the invention. 
     For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section 112, sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.