Abstract:
A wafer container comprising an enclosure portion with a door frame defining an opening for insertion and removal of wafers and a door for insertion into the door frame for closing the opening and sealing with the door frame has an improved elastomeric seal. In a preferred embodiment of the invention an elastomeric seal encircles the door, is partially inset in a groove in the door, and has a cantilevered portion extending laterally outwardly from the door to engage a sealing surface of the door and a laterally displaced sealing surface of the door frame when the door is seated. Thus a seal can be provided that is effected almost totally by flexure of the cantilevered portion rather than by compression of the seal.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to enclosures. More particularly, it relates to sealable enclosure for holding wafers to be manufactured into semiconductors. 
     Semiconductor wafers are subjected to numerous steps during processing. This usually 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 and extra 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 devices is that they are provided with removable doors or closures which seal or are sealed such as by tape when closed. 
     As semiconductors have become larger in scale, that is, as the number of circuits per unit area has increased, contaminants in the form particulates have become more of an issue. The size of particulates that can destroy a circuit has decreased and is approaching the molecular level. Particulate control is necessary during all phases of manufacturing, processing, transporting, and storage of semiconductor wafers. The industry is moving toward processing larger and larger wafers into semiconductors. Three hundred millimeter (300 mm) wafers are now commonplace. 
     Wafer carriers may be made of a variety of materials which in almost all cases comprised thermoplastics. Early containers including, enclosures and closures, were made of highly moldable plastics such as polyethelene, see U.S. Pat. No. 4,248,346, and some held rigid h-bar carriers such as disclosed in U.S. Pat. No. 5,273,159, and some comprise polycarbonate enclosure portions with molded in slots and with softer more resilient covers. See for example U.S. Pat. No. 5,586,658. 
     Such containers typically relied on an enclosure portion to cover contact for providing the sealing of the container. Other containers, primarily for use within semiconductor fabrication facilities, have both a door to enclosure portion seal and also have the capability to sealingly engage to process equipment. Such container have been termed “SMIF pods” (sealed mechanical interface) where the door closes an open bottom of the container portion, or transport modules, where the door closes an open bottom. These containers are subjected to very demanding structural requirements and performance requirements. For example, they must mechanically latch by robotic or manual means and must of course provide exceptional isolation, such as being hermetically sealable simply by closing the door. For containers for 300 mm wafers that are utilized in fabs, front opening modules are being utilized. Conventional seals for both SMIF pods and transport modules have been relatively simple elastomeric seals that are simply compressed between the door and enclosure portion in an axial direction to provide the seal. As such, the seal contact with the door is aligned with the seal contact with the door frame. Such sealing, particularly where polycarbonate is the contacted by the elastomeric seal, tend to stick excessively and provide inconsistent opening, reduced life expectancy of the seal and inadequate sealing. 
     A seal is needed for wafer enclosures that is not subjected to direct compression as it seals. 
     Better performing and longer lasting seals are needed for wafer enclosures. 
     SUMMARY OF THE INVENTION 
     A wafer container comprising an enclosure portion with a door frame defining an opening for insertion and removal of wafers and a door for insertion into the door frame for closing the opening and sealing with the door frame has an improved elastomeric seal. In a preferred embodiment of the invention an elastomeric seal encircles the door, is partially inset in a groove in the door, and has a cantilevered portion extending laterally outwardly from the door to engage a sealing surface of the door and a laterally displaced sealing surface of the door frame when the door is seated. Thus a seal can be provided that is effected almost totally by flexure of the cantilevered portion rather than by compression of the seal. 
     An object and advantage of preferred embodiments of the invention is that a desired sealing force between the door frame and the seal can be easily designed into the cushion by shifting the position of the pedestal portion. 
     A further object and advantage of preferred embodiments of the invention is that the sealing is not provided by compressing an elastomeric seal, rather it is provided by flexing a cantilevered portion by the insertion of the door. 
     A further object and advantage of particular embodiments of the invention is that a very soft seal of high integrity is provided which essentially eliminates sticking between the door and door frame. 
     A further object and advantage of preferred embodiments of the invention is that the seal can be easily replaced when it is worn out or when different sealing characteristics are desired. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a wafer carrier embodying the invention. 
     FIG. 2 is a rear elevational view of a door embodying the invention. 
     FIG. 3 is a top plan view of a door embodying the invention. 
     FIG. 4 is a perspective view of a corner of a door embodying the invention. 
     FIG. 5 is a cross sectional view of a portion of a door and door frame embodying the invention. 
     FIG. 6 is a cross sectional view of a portion of a door and a door frame embodying an alternate embodiment of the invention. 
     FIG. 7 is a cross sectional view of a portion of a door and a door frame embodying an alternate embodiment of the invention. 
     FIG. 9A is a cross sectional view of a seal according to the invention. 
     FIG. 9B is a cross sectional view of a seal according to an alternate embodiment of the invention. 
     FIG. 9C is a cross sectional view of a seal according to an alternate embodiment of the invention. 
     FIG. 9D is a cross sectional view of a seal according to an alternate embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1,  2 ,  3 , and  4 , a wafer container commonly known as a transport module  20  is illustrated and is principally comprised of an enclosure portion  22  and a door  24 . A seal  26  extends around the peripheral portion  28  of the door for sealing engagement with the enclosure portion  22 . The enclosure portion has a plurality of slots  32  into which are placed wafers  34  for containment during transportation or storage. Said wafer enclosure has a door frame  38 , which in the embodiment of FIG. 1, is configured as a flanged structure shaped for receiving the door. The door frame includes a sealing surface  40 , walls  42 , and latch receivers  46 . When used herein, door frame should not be limited to include a separate structure from the enclosure portion nor additional structure on or integral with the enclosure. Rather door frame is hereby defined to be the portion of the enclosure portion which receives the door. The door frame further defines an opening  48  for insertion and removal of the wafers  34 . 
     The door has an axis A 1  and the closure portion has an axis A 2 . For proper insertion of the door into the door frame axis A 1  and A 2  should be aligned. When the door is inserted into the door frame, the door thus moves in an axial direction. When “radial” is used herein, it is intended to refer to direction or orientations which are normal to the axis A 1  or A 2  and can also include, with reference to the seal  26 , any directions which are normal to that particular portion of the seal as opposed to a pure vector outwardly from the door axis. 
     The wafer container  20  utilizes removable door guides  52  on the door to facilitate proper axial alignment of the door with the door frame as well as minimal particle generation for any door-to-door frame contact. On the inside surface  54  of the door are wafer cushions  56  which provide a slightly biased constraint to the wafers when the door is in place. The cushions may be attached suitably at the connection points  58  with plastic snapin connectors. The door enclosure portion may be configured such that the only contact between said components is the seal to door frame engagement and the door guide to door frame contact. Alternatively, supplemental stop portions may be provided in the enclosure portion to allow the door to bottom out when the seal is appropriately flexed. A portion of the exterior door panel  62  is removed in FIG. 1 to disclose the interior space  64  of the door as well as a portion of the latching mechanism  66 . Said latching mechanism may operate as disclosed in U.S. Pat. No. 5,711,427 to David L. Nyseth and owned by the owner of the instant invention. Said patent for the purposes of full disclosure is incorporated herein. 
     Referring to FIG. 5, a detailed cross section of a portion of a door and door frame are shown according to the invention herein. The door  24  is inserted in an axial direction as indicated with the arrow enumerated  69 . The cammed surfaces  71  on the door guides  52  provide initial and final centering effects for the door in the door frame if needed. The door includes a radially inset groove  74  into which the seal  26  is set. The seal is suitably retained in said groove by structural features such as nubs  76  or the like. Other attachments may be used. The seal in an unstressed state would be as indicated in FIG.  9 A and is generally comprised of an inset portion  80  which includes a proximal portion  84  and intermediate portion  86  and a distal portion  88 . The inset portion is moreover a fixed portion  90  and the cantilevered portion is similarly a sealing or exposed portion. 
     Extending from the distal portion  88  of the exposed portion is and opposite side  99  and a first projecting sealing section  96  which projects radially inward protruding in an opposite direction from the intermediate portion  86  is a second protruding section  98  which is shown configured as a pedestal portion. The seal  26  has a greater dimension  150  in a radial direction and a lesser dimension  151  in an axial direction, indicated in FIGS. 9A and 9B. 
     Generally, FIG. 5 shows a door and door frame or a door and enclosure juncture  100 . The contact between the door and the door enclosure as indicated earlier may be limited to the door guide  52  and the door frame as well as the seal  26 . This type of configuration is illustrated in FIG.  6 . Alternatively, the door frame may include seating portions  104  onto which rigid portions of the door  24  may seat in an axial direction. Significantly as shown both in FIG.  5  and FIG. 6, the seal is not in any substantial compression; rather the contact between the seal and the door frame causes a deflection of the cantilever portion. The pedestal portion  98  can be suitably sized to minutely control the contact force between the seal and the door frame. Moreover, the contacts between the door seal contacts  106 ,  108  are radially displaced from the seal enclosure contact  110  in certain embodiments of the invention. The door and seal may be configured to provide some minimal door-to-seal contact that is in radial alignment with the seal to enclosure portion contact  110 , such as by the enlarged distal portion of the seal as illustrated by the dashed lines enumerated  112  in FIG.  5 . 
     An alternative configuration of the seal is shown in FIG.  7 . This seal has the inset portion  80  and a cantilevered portion  82  which is branched into a “Y” configuration with two cantilevered branches  116 ,  118 . Each of the cantilevered branches has a contact surface  120 ,  122  with the door frame and the door respectively. The cantilever branches  116 ,  118  correspond to the protruding sections shown in FIGS. 5 and 6 and thus consist of a first protruding sealing section  96  and a second protruding section  98 . Note that the second protruding sections may or may not be sealing sections in that the principal seal is provided by way of the first protruding section. The second protruding section operates primarily to provide consistent, measured, and precise control of the deflection, and sealing force relative to the first protruding sealing section  96 . 
     Referring to FIGS. 9A,  9 B,  9 C, and  9 D, various other embodiments of the seal are illustrated. The embodiment of FIG. 9B does not have the pedestal portion or the second protruding portion and relies exclusively on the resiliency of the cantilevered portion to provide the desired sealing engagement force. The embodiment of FIG. 9C does not have a first protruding sealing section but rather relies upon the non-protruding surface  126  to seal against the door frame. FIG. 9D illustrates an embodiment in which the first protruding sealing section which engages the door frame extends from the intermediate portion of the cantilevered portion and the second protruding section extends in an opposite direction from the distal portion  88 . 
     In the preferred embodiment, the main structural components of the enclosure portion, particularly the door frame, would be molded of rigid plastic such as polycarbonate. Similarly, the main structural portions of the door, particularly the peripheral portion  28 , similarly may be molded from polycarbonate. The wafer guides may suitably be formed of an abrasion resistant composite plastic such as polyetheretherketone (PEEK) and polytetrafluorethylene (PTFE). The elastomeric seal may be formed of elastomers such as Viton®, available from the Dupont Corporation, or generic ethylenepropylenediene monomer or similar elastomeric materials. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof; and it is, therefore, desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.