Abstract:
A wafer container with the door frame has a magnetic seal that encircles the periphery of the door and has a flexible portion extending laterally outwardly to engage a corresponding magnetic seal around the periphery of the door. Thus the door and container can be provided with a seal that is strong enough to exclude contaminants and also allows easy removal of the door either manually or by a robotic arm.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to enclosures. More particularly, it relates to sealable enclosure for holding wafers to be manufactured into semiconductors.  
         [0002]     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 by tape or externally such as in plastic bagging.  
         [0003]     As semiconductor integrated circuits have become smaller in scale, that is, as the number of circuits per unit area has increased, contaminants in the form of particulates have become more problematic. 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.  
         [0004]     Wafer carriers may be made of a variety of materials which in almost all cases today are comprised of thermoplastics. Early containers including, enclosures and closures, were made of highly moldable plastics such as polyethylene, 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. An example is disclosed in U.S. Pat. No. 5,586,658.  
         [0005]     Such containers typically relied on an enclosure portion that engaged the flexible cover for providing the sealing of the container. Other containers, primarily for use within semiconductor fabrication facilities, have both a rigid door to enclosure portion seal provided by an elastomeric seal and also may have the capability for sealing engagement to process equipment. Such containers have been termed “SMIF pods” (sealed mechanical interface) where the door closes an open bottom of the enclosure portion, or transport modules or FOUPS (Front Opening Unified Pod), where the door closes an open front. 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 or near 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.  
         [0006]     Better performing and longer lasting seals are needed for wafer containers and particularly the containers for larger wafers.  
       SUMMARY OF THE INVENTION  
       [0007]     The substrate container of the present invention provides a magnetic seal or gasket between a door and an enclosure portion. The magnetic seal is formed around the periphery of a door and a door frame by utilization of a magnetic field between the door and the enclosure. The magnetic field is created by a magnet as part of at least of two opposing sealing parts. The door comprises one sealing part on the periphery of the door and the other cooperating part is on the door frame portion of the enclosure. In preferred embodiments, one part comprises a flexible or elastomeric gasket with a magnet or magnetic material therein. The second part has an opposing surface preferably with either a metallic strip or another magnet preferably covered by or embedded in rigid plastic or an elastomeric material. These two surfaces sealing engage each other when the first and second parts are in close proximity, thereby providing a seal for the container. The door is preferably retained to the enclosure by a latch, so the magnetic field strength between the two portions of the magnetic gasket or seal need only be strong enough to create a seal. In a preferred embodiment the door to door frame engagement has a hard stop, preferably hard plastic to hard plastic at which point the sealing part comprising a flexible gasket, extends by way of magnetic attraction to the other sealing part accomplishing a sealing connection between the door and enclosure portion.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective view of a bottom-opening wafer carrier according to the invention.  
         [0009]      FIG. 2  is a perspective view of a front-opening wafer carrier according to the invention.  
         [0010]      FIG. 3  is a of the inner surface of a door to a front-opening wafer carrier according to the invention.  
         [0011]      FIG. 4  is a cross-sectional view of a portion of a door and door frame with a non-engaged seal according to the invention.  
         [0012]      FIG. 4   a  is a detailed perspective cut-away view of a portion of a door according to the invention.  
         [0013]      FIG. 4   b  is a detailed perspective cut-away view of a portion of a container portion according to the invention.  
         [0014]      FIG. 5  is a cross-sectional view of a portion of a door and a door frame with an engaged seal according to the invention.  
         [0015]      FIG. 6  is a cross-sectional view of a portion of a door and a door frame with an alternate seal according to the invention.  
         [0016]      FIG. 7  is a cross-sectional view of a portion of a door and door frame of a SMIF pod with a non-engaged seal according to the invention.  
         [0017]      FIG. 8  is a cross-sectional view of a portion of the door and the door frame of  FIG. 7  with the door encountering a hard stop with the enclosure portion according to the invention.  
         [0018]      FIG. 9  is a cross-sectional view of the portion of the door and the door frame of  FIG. 8  with the first sealing part comprising a flexible gasket extending into a sealing engagement with a second sealing part. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]     Prior art  FIGS. 1 and 2  show a bottom-opening SMIF pod  20  and a front-opening transport module or FOUP  30  respectively for which the invention is highly suitable. Each sealable enclosure has a enclosure portion  34  and a cooperating door  36 . The SMIF pod  20  also has a separate wafer carrier  38  which is a H-bar carrier, well known in the art, which seats on the top surface  40  of the door  36 . A plurality of wafer supports  39  are present in each of both substrate containers.  
         [0020]     Each enclosure portion  34  and each enclosure has a top side  46 , a front side  48 , and a bottom side  50 . In the SMIF pod the bottom side  50  is open for receiving the wafer carrier  38  and the door  36 . In the transport module  30  the front side  48  is open and is closed by the door  36 . A recessed lip  51  is located at the periphery of enclosure portion  34 .  
         [0021]     The doors have an inwardly facing side  52 , an outwardly facing side  53 , and a periphery  54  including four sidewalls  55 . Each of the doors  36  comprise an enclosure  56  with an open interior  58  which contains a latching mechanism  60 , a portion of which is shown in  FIGS. 1 and 2 . The latching mechanism includes a latching portion  62  which is extendable out of slots  66  to engage into latching portion receivers  68  located in the door frame portion  74  of the enclosure portion  34 . Door guides  75 , may be utilized to provide guidance of the door into the door frame  74 . Such door guides are described in detail in U.S. Pat. No. 6,464,081 owned by the owner of this application. Said patent is incorporated herein by reference.  
         [0022]     On the inside surface  54  of the door are wafer cushions  80  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  82  with plastic snapin connectors or other suitable means known in the art. The door enclosure portion may be configured such that the only contact between these 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 in an extended position. A portion of enclosure  56  is removed in  FIG. 2  to disclose a portion of door-latching mechanism  66 . This 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 present invention. For the purposes of full disclosure, this patent is incorporated herein by reference.  
         [0023]      FIGS. 4, 4   a ,  4   b ,  5 , and  6  show sealing devices  100  in different configurations. Door  36  is inserted in an axial direction, the “z” direction on the x-y-z coordinate system, as indicated by arrow  69 . This is also the direction in which wafers are inserted. Sealing device  100  has a first sealing part  102  attached to door  36  and a second sealing part  104  attached to container enclosure  34 . First sealing part  102  of sealing device  100  includes a base  110 , an extendable and flexible member  112 , and engagement surface  114 , and an embedded, preferably overmolded, magnet  116 . Second sealing part  104  of sealing device  100  includes a base  120  and an overmolded ring  122 . Overmolded ring  122  may be made of any material capable of magnetically being attracted to overmolded magnet  116 , such as another magnet, a metal, or the like, that is, a magnetically attractable material. As illustrated in  FIG. 4   b , the ring of magnetically attractable material  122  may be multiple pieces  123  overmolded into the container portion. Alternatively, at least one of first sealing part  102  and second sealing part  104  may be plastic magnets. First sealing part  102  and second sealing part  104  are positioned opposite each other so that they engage easily when in close proximity.  
         [0024]     Overmolding in the context of wafer container components is illustrated in U.S. Pat. Nos. 6,871,741 and 6,808,668 both owned by the owner of this application. Such techniques are highly suitable to the sealing structure disclosed herein. Said patents are incorporated herein by reference.  
         [0025]     Sealing device  100  engages when first sealing part  102  and second sealing part  104  reach a critical proximity, which is a function of the magnetic field strength. For example, when first sealing part  102  and second sealing part  104  are initially aligned, but not in close proximity, sealing device  100  is in a non-engaged state, as depicted in  FIG. 4 . As first sealing part  102  and second sealing part  104  are moved closer together, engagement surface  114  eventually engages sealingly with second sealing part  104  as depicted in  FIG. 5 . The magnetic field strength is strong enough to sealingly engage door  36  and enclosure portion  34 , yet it is not so strong that door  36  may not be removed easily when door  36  is removed from enclosure portion  34 . Door  36  is retained to enclosure portion  34  by door-latching mechanism  66 , so the magnet field strength need not be strong enough to retain door  36 , but only strong enough to provide an adequate seal. Preferably, there is a hard stop  115  defined such as a non-gasket door surface  117  contacting a non-gasket door frame surface  119 . The surfaces comprising the hard stop are preferably positioned such that the first sealing  102  must extend to engage and seal with the second sealing part  104  when the hard stop is accomplished.  
         [0026]     The placement of the overmolded magnet  116  and overmolded ring  122  may be reversed, as shown in  FIG. 6 . In this embodiment, first sealing part  102  is attached to container enclosure  34  and second sealing part  104  is overmolded directly within the door  36 . Even though the positions of first sealing part  102  and second sealing part  104  are reversed, they otherwise function as described above for the configurations shown in  FIG. 5  and  FIG. 6 .  
         [0027]     Additionally, the magnet may be embedded and fixed with respect to one of the door and enclosure portion and the other of the door and enclosure portion may have the sealing part with an extendible portion and a magnetically attractable material attached or contained or embedded therein. Said magnetically attractable material may be a single piece, multiple discrete pieces, or multiple particles disbursed throughout the flexible sealing part.  
         [0028]     In certain embodiments the two engagement surfaces may both be more rigid, with neither one being elastomeric, rather sufficient sealing being provided by, for example rigid plastic to rigid plastic contact, the plastics being similar or dissimilar. For examples, polycarbonates and fluoropolymers such as PFA (perfluoroalkoxy), ABS, PEEK and other plastics known to those in the art may be suitable. Additionally the sealing part can have an extendible elastomeric portion and a rigid plastic that contacts and seals with the cooperating surface.  
         [0029]     In use, first sealing part  102  and second sealing part  104  function as gaskets and a cooperating sealing surface. The overmolded magnet  116  and overmolded magnetically attractable material  123  cause engagement surface  114  to engage sealing surface  127  of second sealing part  104  as a result of magnetic attractive forces. Flexible member  112  of first sealing part  102  stretches when engagement surface  114  is positioned close enough for sealing engagement with second sealing part  104  of sealing device  100 . The magnetic attractive forces, however, are only so strong that the engagement surface  114  and second sealing part  104  may be readily uncoupled manually or by a robotic arm when door-latching mechanism  66  is uncoupled and door  36  is removed from enclosure portion  34 .  
         [0030]     Referring to  FIGS. 7, 8 , and  9 , an embodiment in the context of a SMIF pod with a door  140  and container portion  142  are illustrated. The container base or door  140  has a first sealing part  144  that includes an elastomeric flexible gasket  146  with a base portion  147  positioned in a recess or slot  148  in the door. An extendable portion  149  may be configured as a bellows or other elongatable configuration. The first sealing part preferably embeds, such as by overmolding, a magnet  150 . A sealing surface  152  faces the opposing sealing surface as the door and container portion are brought together. The first sealing part has a retracted position as illustrated in  FIGS. 7 and 8  as well as an extended position and an engagement position as illustrated in  FIG. 9 . A hard stop  115  similar to that described with reference to  FIGS. 4 and 5  is also present.  
         [0031]     As illustrated in  FIG. 6 , the magnet or the magnetically attractable material may be directly embedded in the principle material comprising the container portion, the door frame, or door enclosure, such as polycarbonate. In such a case the “first sealing part” or “second sealing part” is an integral portion of the door or enclosure portion as opposed to being part of an assembly. In other embodiments, both the first sealing part and second sealing part can have extendible portions  149 .  
         [0032]     The container portion  158  has a second sealing part  160  comprising a sealing surface  162  and has magnetically attractable material  166  therein, preferably embedded therein such that only plastic is exposed.  
         [0033]     The sealing components in this embodiment function as follows. In  FIG. 7  the first sealing part, in particular the extendable portion is in it retracted state with a magnetic field  170  not having any magnetically attractable components therein. In  FIG. 8 , the container portion has been placed on the door such that the magnetic material of the second sealing part is within the magnetic field  170  of the first sealing part. This causes an extension of the first sealing part toward the second sealing part to the sealing engagement constituting as shown in  FIG. 9 . When the door is removed, or the container portion lifted, the extendable portion is at or near its maximum position such that the sealing surfaces separate after minimal separation of the door and container portion.  
         [0034]     The main structural components of the enclosure portion, particularly the door frame, may be molded of rigid plastic such as polycarbonate. Similarly, the main structural portions of the door, particularly the peripheral portions  54 , 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.  
         [0035]     The present invention may be embodied in other specific forms without departing from its spirit or essential attributes; the embodiments described are thus in all respects illustrative and not restrictive. The appended claims rather than to the foregoing description indicate the scope of the invention.