Abstract:
Components, systems, and methods for maintaining an extremely dry environment within substrate containers formed of polymers provides supplemental exterior gas washing of the substrate container to minimize permeation of moisture and oxygen through the polymer walls of the container and to control desorption of water entrapped in the polymer walls of the container.

Description:
RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Application No. 61/014,709 filed Dec. 18, 2007, which is incorporated herein in its entirety by reference. 
     
    
     Field of the Invention 
       [0002]    This invention relates to substrate containers and maintaining dryness and minimizing contamination within the interior of such containers. 
       BACKGROUND OF THE INVENTION 
       [0003]    It has been realized that moisture within the polymer walls of reticle pod or wafer containers, as well as moisture permeating through the polymer walls, is a source of contamination of substrates contained in such containers. 
         [0004]    During transportation, storage, or pauses in subsequent manufacturing processes, semiconductor wafers which are stored in special containers, such as SMIF pods (acronym for standardized mechanical interface), and FOUPs (acronym for front opening unified pod). Depending on a number of factors such as size of production run and cycle time, wafers may sit in such containers for a substantial time between processing steps. During this time processed wafers are affected by ambient moisture, oxygen and other AMC&#39;s (“airborne molecular contaminants”) detrimental to production yield. 
         [0005]    For instance, moisture can cause uncontrolled native oxide growth, formation of haze and corrosion, whereas oxygen is known to affect Cu-interconnect reliability. Experimental data and computational studies have shown that closed FOUPs, with wafers inside can be effectively purged with a continuous flow of nitrogen through an inlet port on the lower base of the shell or the FOUP&#39;s door. It is known that a gentle flow of nitrogen at about 4 liters per minute provides for significant reduction of the oxygen and moisture level inside a loaded FOUP, down to−1% RH and 1% of  0   2  in just in 4 to 5 minutes. Experimental data shows also that termination of the nitrogen purge flow can cause very rapid, within minutes, increase of moisture concentration, levels greater than 1% inside the FOUP. This effect is believed to be caused by moisture permeation through the walls of the FOUP and by moisture desorption from the polycarbonate walls of the FOUP. 
         [0006]    A better system and process is needed to better protect substrates, for example wafers, against ambient moisture and oxygen. 
       SUMMARY OF THE INVENTION 
       [0007]    In certain embodiments, a double purge of loaded substrate containers, for example FOUPs, during their storage and intrabay transportation such as with the aid of PGV (personal guided vehicle) is provided. The double purge may includes a flow of clean dry air (“CDA”), or other purge gas directed or confined to the outside of the substrate container which prevents or minimizes permeation of moisture into the substrate container and effects progressive drying of the polymer confinement walls which may be, for example, polycarbonate. Conventional interior purging, such as by nitrogen, of the interior of the FOUP will prevent oxygen build-up and provides drying of the confinement walls from the interior. 
         [0008]    Partition walls or shrouds inside the storage stockers for the substrate containers will ensure effective circulation of CDA. Similar shrouds and partition walls inside intra bay mini-storages and enclosures on purge stations will provide effective CDA usage also. PGVs equipped with re-chargeable low-pressure vessels filled with CDA and N2 may provide double purging for FOUPs in transit. 
         [0009]    In embodiments of the invention, a system for maintaining an extremely dry environment within substrate containers formed of polymers provides supplemental exterior gas washing of the substrate container exterior to minimize permeation of moisture and oxygen through the polymer walls of the container and to further provide for desorption of water entrapped in the polymer walls of the container. 
         [0010]    Specific shrouds and/or purge gas directing plates can be provided downstream from discharge nozzles as part of stockers to control and contain the exterior purge. Shrouds and double walls may be provided to wafer container to provide a confined pathway for the exterior purge gas wash. 
         [0011]    A feature and advantage of the invention in certain embodiments provides a substrate container with a wall cavity to provide an inner wall with exterior purge capabilities for an outwardly facing surface of said inner wall. Said wall cavity may be substantially closed with a restricted inlet area, for example, less than 1 square inch. Also the outlet area may be restricted, for example, less than one square inch. The inlet and outlet may have a further restriction member in the inlet and/or outlet, for example a check valve or filter. A feature and advantage of the invention in certain embodiments provides a stocker with substrate container shroud not fixed to the wafer container providing a gap of about 0.25 inch to about two inches from the exterior surface of the wafer container. 
         [0012]    A feature and advantage of the invention in certain embodiments provides a substrate container that has in interior containment wall with an exterior shroud fixedly attached to the wafer container providing a gap of about 0.25 inch to about two inches from the exterior surface and creating a cavity between the fixedly attached shroud and the of the interior containment wall whereby a exterior purging gas can be provided to the cavity. 
         [0013]    In an embodiment, the gap is less than 2 inches for the majority of the inside surface of the shroud. 
         [0014]    A feature and advantage of certain embodiments of the invention is a method of modifying substrate containers by adding exterior shroud pieces to the substrate container to provide a cavity between an exteriorly facing surface of a containment wall of the substrate container and the shroud wherein an exterior purging gas may be provided thereto. 
         [0015]    A feature and advantage of certain embodiments of the invention provides a purging outlet from a substrate container wherein purging gas that is circulated within the interior of the substrate container is redirected after the purging gas leaves the interior to wash the exterior surface of the substrate container. 
         [0016]    A feature and advantage of certain embodiments of the invention provides a substrate container with deflector pieces at the purging outlet whereby purging gas that is circulated within the interior of the substrate container is redirected after the purging gas leaves the interior to wash the exterior surface of the substrate container. 
         [0017]    A feature and advantage of certain embodiments of the invention provides a substrate container with purging outlets distributed over the container and with the outlets exiting to the exterior of the container the outlets redirecting the exiting purge gas in a direction parallel to the exterior surfaces of the container. Such purge outlets may have check valves therein to prevent flow of gases into the interior when the purging is not occurring. 
         [0018]    A feature and advantage of certain embodiments of the invention is a substrate container with a plurality of purging inlets, at least one purge inlet directed into the interior of the substrate container and at least one purge inlet directed to washing the exterior surface of a wall defining the interior containment of the substrate container. 
         [0019]    A feature and advantage of certain embodiments of the invention is a substrate container with a plurality of purging inlets, at least one purge inlet directed into the interior of the substrate container and at least one purge inlet directed to washing the exterior surface of a wall defining the interior containment of the substrate container. 
         [0020]    A feature and advantage of certain embodiments of the invention provides for deflector pieces at the purging outlets whereby purging gas that is circulated within the interior of the substrate container is redirected after the purging gas leaves the interior to wash the exterior surface of the substrate container. Such deflectors can be attached or fixed to the substrate container or may be separate therefrom, such as part of the stocker or enclosure for the container. 
         [0021]    A feature and advantage of certain embodiments of the invention is that the purge gas that is highly concentrated (such as very clean and very dry air) can optimally be utilized by dispersing it in close proximity to the outside surface of a substrate container thereby minimizing moisture permeation and maintaining minimal moisture in the polymer shell of the reticle pod and accelerating diffusion from the substrate container surface 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0022]      FIG. 1  is a diagrammatic view of a reticle pod stocker with purging features in accord with the invention herein. 
           [0023]      FIG. 2  is a diagrammatic view of a wafer container, stocker with purging features in accord with the invention herein. 
           [0024]      FIG. 3  is a perspective view of a reticle SMIF pod in accord with the invention herein. 
           [0025]      FIG. 4  is a cross sectional diagrammatic view of the reticle pod of  FIG. 3  connected to purging systems in accord with the inventions herein. 
           [0026]      FIG. 5  is another diagrammatic view of a reticle SMIF pod in accord with the invention herein. 
           [0027]      FIG. 6  is a diagrammatic view of a SMIF pod in accord with the invention herein. 
           [0028]      FIG. 7  is a diagrammatic view of a SMIF pod in accord with the invention herein. 
           [0029]      FIG. 8  is a detailed cross sectional view of a purge deflector with a check valve in accord with the invention here in. 
           [0030]      FIG. 9  is cross sectional view of a SMIF pod in accord with the invention herein. 
           [0031]      FIG. 10  is a perspective exploded view of a SMIF pod for semi-conductor wafers in accord with the invention herein. 
           [0032]      FIG. 11  is a perspective view of a front opening wafer container in accord with the invention herein; for example a 300 millimeter front opening unified pod, a FOUP. 
           [0033]      FIG. 11   a  is bottom view of the FOUP of  FIG. 11 . 
           [0034]      FIG. 12  is an exploded view of a front opening substrate container in accord with the invention herein. 
           [0035]      FIG. 13  is a cross sectional view of wall detail of a substrate container in accord with the invention herein. 
           [0036]      FIG. 14  is an alternate view of the cross sectional detail of a substrate container in accord with invention herein. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    Referring to  FIG. 1 , an enclosure  20  is illustrated configured as a reticle SMIF pod stocker having purge gas supplies  24  and  26 . Alternatively, the substrate container may be wafer containers such as those known as FOUPs (front opening unified pods) and FOSBs (front opening shipping boxes). In such stockers clean dry air or very clean dry air may be provided to the enclosure. Alternatively a pure inert gas such as nitrogen may be provided. The stocker has receiving regions  40  and  42  where reticle SMIF pods seat on shelves  44 ,  46  the reticle SMIF pods  50  have purge inlets at the bottom of said reticle pods whereby a purging gas is provided into he interior of said reticle pods. Said purging gas may be discharged through filters  60  in the base of the reticle pod into the ambient environment  64  of the stocker additional exterior surface purge gas is provided by purge outlets, such as nozzles  68 ,  70 , which are directed towards the exterior of the reticle SMIF pod. Shrouds or directing plates  75 ,  76 ,  77  may be utilized downstream of the nozzles to direct the air or gas flow to the exterior surface of the pod This concentrated purge gas provides drawing of the polymer shell of the reticle pods and prevents permeation of moisture therein and drys out the polymer shell. The enclosure may have partitions  74  to isolate said reticle pods to allow maximum concentration of the purged gas provided for the exterior washing of said pods. An additional purge gas outlet  78  may be provided in the interior for providing generally clean air into the interior of the reticle pod stocker. See PCT/US2007/014428 incorporated herein by reference for explanation and descriptions of CDA and extra clean dry air. 
         [0038]    Note that the various purge gases provided may be optimally composed and have varying levels of dryness and/or cleanliness for the specific intended function, that is, interior purging, exterior purge gas washing, or providing the ambient atmosphere in the stocker. 
         [0039]    Referring to  FIG. 2 , a further enclosure  100  is illustrated having shelves  102 ,  104 . Said shelves having purging outlets  106 ,  108  and purging exhaust receivers  110 ,  112  for receiving the purged gas after it has circulated through the wafer container. Wafer containers such as SMIF pods or FOUPs  120  may be placed on said shelves to seat on the respective purging outlets and purging exhaust fittings. Additionally, shrouds  130  are provided that are movable upwardly and downwardly to generally enclose the substrate containers providing a restrictive interior space whereby a specific purging gas may be provided to effectively the wash the exterior of the substrate container  120 . Said purging gas may be exhausted between the juncture of the shroud and shelf or through other venting or outlet exhaust means. Various supplies of purging gas may be provided as illustrated by supplies  142 ,  144 ,  146  and purge gas lines  147 ,  148 ,  149 . Such supplies may be different gasses such as nitrogen versus air and may be provided with varying degrees of cleanliness and/or dryness as desired or appropriate. The enclosure of  FIG. 2  may be portable as illustrated by wheels  150  to transport the substrate containers within a fabrication facility typically intermediate processing steps. 
         [0040]    Referring to  FIGS. 3 and 4 , a SMIF pod is illustrated generally configured as a reticle SMIF pod  160 . Said reticle SMIF pod is generally comprised of a shell portion  162 , a door  163 , and a shroud  164 . The shroud  164  is configured to overlay in juxta position to the outside surface  168  of the shell portion. Said shell portion operates as a containment for the reticle contained therein. Referring specifically to  FIG. 4  the reticle  172  is illustrated by dashed lines and is supported by reticle supports  174 ,  176 . The door has a pair of purge inlets  182 ,  184  which are connected to the interior  186  of the reticle pod as defined by the shell and the door. Purge nozzles  190 ,  192  inject purge gas into the interior of said reticle SMIF pod. In this configuration the purge gas is exhausted through a filter  194  positioned centrally in the door  163 . The shroud  164  has a further purge inlet  198  which leads into the space  200  defined between the shroud  164  and the exterior surface  168  of the shell. Said purge gas injected into said space  200  and is conveyed along and adjacent to said exterior surface, in a direction parallel to said exterior surface, and is directed to and follows the contours of said exterior surface as constrained by said shroud. The purge gas may be exhausted at the openings  204 . T gas flow is illustrated generally by the arrows in the figures and particularly here in the space  200 . Different purge gas sources  208 ,  210  can be provided for the purge gas providing varying compositions and/or cleanliness and/or dryness. 
         [0041]      FIG. 5  illustrates an alternative view of a SMIF pod in which the purge gas is injected into the interior of the SMIF pod to be exhausted out an outlet  220  in the SMIF pod shell portion  162 . Said purge gas is thus circulated in the interior of the SMIF pod and then exits and is forced to travel along the exterior surface  168  of the shell as directed by the shroud  164 . 
         [0042]    Referring to  FIG. 6 , a further embodiment of a SMIF pod  250  is illustrated. The SMIF pod has a shell portion  252 , a door  254 , with an interior  256 . The door and the shell portion define an interior  260  for the containment of the reticle  264 . The door has, in this embodiment, two purge inlets  270 ,  272  that lead into the interior of the reticle pod where the reticle is contained. A third purged inlet  276  leads into the interior of the door. The door has a purge outlet  278  whereby purge gas injected into the door interior  256  is exhausted out of the door. In SMIF pods, the doors are positioned at the bottom of the pods; in FOUPS and FOSBs, the doors are positioned at an open front of the container portion, see  FIG. 11 . Such FOUP and FOSB doors will often have open interiors that may similarly be purged. In the configuration of  FIG. 6 , the purge gas injected into the interior of the reticle pod, where the reticle is stored, is exhausted out an opening  282  in the shell. Said opening having a filter  284  disposed therein as disclosed in US 2006/0266011, incorporated herein by reference. The exhaust gas for the interior of the reticle pod is then forced along the exterior surface of the shell portion by the shroud  286 . The purge gas supply  290  may have separate portions  292 ,  294  for providing purge gas of different compositions and/or cleanliness and/or dryness. 
         [0043]    Referring to  FIG. 7 , a further SMIF pod  300  is illustrated. The SMIF pod generally comprises a door  302  and a shell portion  304 . The door has purge inlets  306 ,  308  that are connectable to purge sources and that inject the purge gas into he interior  310  of the SMIF pod  300 . In this configuration the shell has a plurality of outlets to exhaust the purge gas and a plurality of deflectors  320  positioned at each of the shell outlets. The deflectors deflect and direct the exhaust gas leaving the interior of the SMIF pod to wash the exterior surface  324  of the shell. Such an arrangement is also suitable for other substrate containers, such as wafer containers, see below. 
         [0044]    Referring to  FIG. 8  a cross sectional detail is illustrated of a configuration of the deflector, said deflector  320  is T-shaped with a threaded end  324  having a conduit pathway  326  extending through and exiting in a lateral direction a check valve  328  is appropriately putted in the outlet to provide for one-way outlet flow only. This may be on the SMIF pods or wafer containers described herein. 
         [0045]    Referring to  FIG. 9 , a further embodiment of a SMIF pod  400  is illustrated and is comprised generally of a door  402  and a shell portion  404 . The shell portion comprises an inner wall  406  and an outer wall  408 . The inner wall has an outwardly facing surface  410 . The SMIF pod has, in this configuration, four purge ports and inlet port  414  configured to inject purged gas into the interior  416  of the reticle pod to be exhausted out the exhaust port  420 . Said ports are suitably located in the door. Substrate support structure  424  is provided on the door and can be configured either as a support for reticles or to position a conventional h-bar wafer carrier. The shell portion seals with the door by way of seals  430  and  432 . The secondary seal  432  provides containment of the space  436  intermediate the inner shell wall and the outer shell wall. An additional purge port  442  is provided to inject a purge gas in the space between the inner shell portion and the outer shell portion. An additional exhaust port  446  is provided to provide an exit of the purged gas exhausted from the space intermediate the wall portions. Although this door is not shown in  FIG. 9  to have an interior as illustrated in  FIG. 6  and  FIG. 7  it is understood by those knowledgeable in the art that said doors would be feasible in the  FIG. 9  configuration and should be included and considered as a embodiment of the invention herein. 
         [0046]    Referring to  FIG. 10 , a conventional SMIF pod  500  is a illustrated with a shell portion  502 , a door  504 , and an H-bar wafer carrier  506 . The door has an internal latch mechanism  510  that will engage with the inside purify of the shell portion  502  to secure the door in place as is conventional with SMIF pods. The door also has support structure  512  to properly position the h-bar  514  of the carrier thereon. Additional purge ports  520  are positioned in the bottom of the door to be engaged from below the door. This SMIF pod may have the upper shell portion configured as illustrated in  FIG. 9  and may have the door as illustrated in either  FIG. 9  or the figures illustrating doors with the open interiors, see  FIGS. 6 and 7 . 
         [0047]    Referring to  FIG. 11 , a front opening pod  600  is illustrated. Such pods are often known as front opening unified pods (FOUPs) and are utilized for storing 300 millimeter wafers intermediate process steps. The container comprises generally a container portion  602 , a door  604  with latch mechanisms, and latch mechanisms key holes  606  in the front of the door. Said door sealingly engages to the shell portion  602  to create a hermetic interior. A bottom side is illustrated in  FIG. 11  a and has an industry standard three-groove kinematic coupling  624  positioned thereon. Purge ports  630  may be positioned on the bottom base of the shell portion or are alternatively positioned on the front door as illustrated by the dash lines on  FIG. 11  with the numeral  634 . The shell portion of the container of  FIG. 11  may have a double wall configuration as illustrated in  FIGS. 13 and 14 . Wafers are contained within the interior  644  of the wafer container and would be conventionally purgeable. An additional supplemental wall  650  may be provided to provide a space  658  between the inner wall  660  and the outer wall  655 . The inner wall has an exteriorly facing surface  662  which is exposed to the interior purged gasses, as indicated by the arrows, and may circulate within the interior between the double wall sections to provide a drying effect to the polymer interior wall and prevent permeation of moisture inwardly. The purge gas can be exhausted from the interior through a port  670  with a check valve  672  as illustrated in  FIG. 13  or can be discharged by way of a separate purge port position in the base of the container portion, see  FIG. 14 . Said port could be as indicated on  FIG. 11 , as illustrated by the dashed lines enumerated with  670 ,  672 . Rather than have the space  658  within the double wall of the FOUP defining a secondary sealed enclosure, such as is illustrated in the SMIF pod of  FIG. 9 , said double wall may be configured as a shroud as illustrated in  FIG. 11 . In either case a purge gas is provided and directed along the exterior facing surface of the wall portions that define the confined interior where the wafers are contained. 
         [0048]    Referring to  FIG. 12 , a configuration is illustrated that would be appropriate for providing the double wall section with sealed interior spaces. This configuration has an exterior shell portion  802 , an interior shell portion  804 , and a door  806 . When assembled a gap is provided between the outer shell and the inner shell with said space between said shells being purgeable to accomplish the functions as described above. Similarly the interior of said container also would suitably would purgeable. Front opening containers as such are typically have machine interfaces configured as threes groove kinematic coupling  812 .