Abstract:
A purging station with a substrate container receiving zone having at least one upwardly extending purging nozzle. The nozzle has a circular engaging lip. The substrate container has support means for at least one substrate and a purge port assembly that includes an externally facing sealing flange facing downward from the container. The sealing flange has a central aperture and a cantilevered flange portion that engages with the circular engaging lip of the nozzle. The weight of the substrate container on the nozzle carried by the canilevered portion of the flange causes bending of the flange for a resilient soft seal.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/892,196, filed Feb. 28, 2007; this application is also related to U.S. patent application Ser. No. 11/396,949; filed Apr. 3, 2006, U.S. Provisional Application No. 60/668,189 filed Apr. 4, 2005, and U.S. Pat. No. 7,328,727 issued Feb. 12, 2008, all of which are incorporated herein in their entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to substrate carriers used in semiconductor manufacturing and more particularly to transportable and shippable reticle/photomask carriers and purging systems for controlling the environment in such carriers. 
       BACKGROUND OF THE INVENTION 
       [0003]    The processing of silicon wafers for semiconductor applications typically includes photolithography as one of the process steps. In photolithography, a wafer surface with a deposit of silicon nitride is coated over with a light-sensitive liquid polymer or photoresist and then selectively exposed to a source of radiation using a template with a desired pattern. Typically, ultraviolet light is shone through or reflected off a surface of a mask or reticle to project the desired pattern onto the photoresist covered wafer. The portion of the photoresist exposed to the light is chemically modified and remains unaffected when the wafer is subsequently subjected to a chemical media that removes the unexposed photoresist leaving the modified photoresist on the wafer in the exact shape of the pattern on the mask. The wafer is subjected to an etch process that removes the exposed portion of the nitride layer leaving a nitride pattern on the wafer in the exact design of the mask. 
         [0004]    The industry trend is towards the production of chips that are smaller and/or with a higher logic density necessitating even smaller line widths on larger wafers. Clearly, the degree of fineness to which the surface of the reticle can be patterned and the degree to which this pattern can be faithfully replicated onto the wafer surface are factors that impact the quality of the ultimate semiconductor product. The resolution with which the pattern can be reproduced on the wafer surface depends on the wavelength of ultraviolet light used to project the pattern onto the surface of the photoresist-coated wafer. State-of-the-art photolithography tools use deep ultraviolet light with wavelengths of 193 nm, which allow minimum feature sizes on the order of 100 nm. Tools currently being developed use 157 nm Extreme Ultraviolet (EUV) light to permit resolution of features at sizes below 70 nm. 
         [0005]    The reticle is a very flat glass plate that contains the patterns to be reproduced on the wafer. Typical reticle substrate material is quartz. Because of the tiny size of the critical elements of modern integrated circuits, it is essential that the operative surface of the reticle (i.e. the patterned surface) be kept free of contaminants that could either damage the surface or distort the image projected onto the photoresist layer during processing leading to a final product of unacceptable quality. Typically, the critical particle sizes are 0.1 μm and 0.03 μm for the non-patterned and patterned surfaces respectively when EUV is part of the photolithography process. Generally, the patterned surface of the reticle is coated with a thin, optically transparent film, preferably of nitrocellulose, attached to and supported by a frame, and attached to the reticle. Its purpose is to seal out contaminants and reduce printed defects potentially caused by such contamination in the image plane. 
         [0006]    However, extreme EUV utilizes reflection from the patterned surface as opposed to transmission through the reticle characteristic of deep ultraviolet light photolithography. At his time, the art does not provide pellicle materials that are transparent to EUV. Consequently, the reflective photomask (reticle) employed in EUV photolithography is susceptible to contamination and damage to a far greater degree than reticles used in conventional photolithography. This situation imposes heightened functional requirements on any reticle SMIF pod designed to store, transport and ship a reticle destined for EUV photolithography use. 
         [0007]    It is well known in the art that unnecessary and unintended contact of the reticle with other surfaces during manufacturing, processing, shipping, handling, transport or storage will likely cause damage to the delicate features on the patterned surface of the reticle due to sliding friction and abrasion. Likewise, it is generally accepted by those skilled in the art that any particulate contamination of the surface of the reticle can potentially compromise the reticle to a degree sufficient to seriously affect the end products of processes that use such a flawed reticle. In this regard, the art has developed innovative approaches to locate and support the reticle in reticle containers so as to reduce or eliminate sliding friction and consequent abrasion of the reticle and the resultant generation of contaminating particulates. In recognition of the need to maintain a controlled environment around the wafer during storage, processing and transport, the prior art has evolved approaches to isolation technology that allows for control of the environment in the immediate vicinity of a wafer by providing for a container so that it can be kept relatively free from incursion of particulate matter. 
         [0008]    Typically, containers are provided with standardized mechanical interfaces that allow automatic manipulation of the container by processing machinery. Such containers can hold photomasks of up to 200 mm and are designated standard mechanical interface pods, or SMIF-Pods. Even with such a controlled environment, migration of particulates that may be present inside the controlled environment is still possible due to pressure changes of the air trapped in the controlled environment or turbulence of the trapped air brought on by rapid movements of the container and/or by disturbing the trapped air volume. For example, thin walled SMIF pods may experience wall movement due to altitude related pressure changes causing the trapped air inside the controlled environment to be displaced. Temperature changes can set up convection currents within the container. Dimensional changes of the container and its components due to pressure fluctuations can lead to compromising the sealing between cover and door of the carrier and incursion of particulates within the carrier. Prior art approaches contemplate a breathing apparatus between the external environment and the internal controlled volume of air. The breathing apparatus provides a path for the air to flow. Prior art breathing apparatus may include a particulate filter to block the entry of particulates from the external environment into the controlled environment of the carrier. 
         [0009]    Those skilled in the art will appreciate that particulate contaminants are but one half of the equation. Equally important are gas-phase contaminants or airborne molecular contaminants (AMC) due to ambient air venting or leaking into or getting trapped in a hermetically sealed system. For example, at a suitable dew point temperature, the moisture in the air will condense out of the air and some of it may get deposited onto the reticle. Even with a perfectly sealed container, there is the possibility of air entering into the system when the reticle is removed from and replaced within the container during processing. Water vapor condensing onto the patterned surface of the reticle can interfere with the optics just as a solid particulate would. Other sources of gas-phase or vapor contamination that are believed to be significant are solvent residues resulting from reticle/pod cleaning operations during the photomask lifecycle, chemical agents generated by out-gassing from the structural components of the carrier and chemical agents that enter into the carrier from the ambient atmosphere by breaching the hermetic sealing arrangement between the carrier shell and the carrier door. 
         [0010]    Multiple contamination species are thought to be the largest contributors to gas-phase contamination. These include NH 3  (ammonia), SO 2  (sulphur dioxide), H 2 O (moisture) and condensable organics C6-C10. Depending on the photolithography system, a photomask can be exposed to a laser light source of a wavelength that can range from 436 nm to 157 mn. Currently, 193 nm lasers are quite common. The energy of the laser can initiate chemical reactions that precipitate defect formation and propagation on the surface of the reticle. For instance, some of the chemical species are altered to form highly reactive species such as SO 4   2−  and NH 4   + . Some of these chemicals, such as acids for instance, are reactive with glass and can damage the reticle by etching it to create a haze on the patterned surface. The bases can create resist poisoning. The condensable organics can lead to SiC formation. In general, all of the contaminants can be considered to result in the same effect: crystal growth that degrades the functionality of the reticle. In this respect, the current thinking is that moisture or water is one of the key ingredients required for crystal growth. Essentially, water combines with some of the aforementioned contaminants to form the salts are generally clubbed together under the rubric of crystal growth. Prior art use of dessicants, for example, cannot ameliorate this problem because they cannot reduce the concentration of moisture to low enough levels to prevent salt (or crystal) formation. Likewise, purging a reticle carrier with clean dry air (CDA) or other dry gas may not reduce the moisture concentration to the levels required to avoid crystal growth. There is therefore a need for a contamination control mechanism at each stage of the reticle life cycle. 
         [0011]    One of the approaches commonly employed in the art to ameliorate the effect of the chemical contaminants is periodic reticle/mask cleaning. The mean time between such cleans (MTBC) can approach, for example, approximately 8000 wafers in a 193 nm exposure tool. The threshold of the MTBC is set to prevent mean time between defects (MTBD) printed on the wafer using the reticle/mask. However, there is a limit to the number of such ‘cleans’ a reticle/mask can be subject to before resolution is degraded beyond functionality and the mask must be scrapped. In view of the above, one of skill in the art will recognize the need to ensure that the reticle environment within the carrier remains clean during storage, transportation, manipulation as well as during the standby condition when the carrier is empty of the reticle. While desirable, it is generally infeasible to construct a hermetically sealed environment that is absolutely impervious to incursion by AMCs or other contaminants. It is also infeasible to continuously purge the reticle carrier especially when the reticle and reticle carrier have to be transported or shipped. 
         [0012]    Although purging solutions, such as disclosed in the related applications referenced above, have greatly controlled the incursion, concentration and rate of accumulation of AMCs within the photomask carrier, further improvement is desirable. Accordingly, what is needed is system, structure, or device for further ameliorating the incursion, concentration and rate of accumulation of AMCs within the photomask carrier to levels that preclude or significantly reduce the formation of crystalline salts and generally minimize the presence of any contaminants on the reticles. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention, in certain embodiments, provides a reticle/mask carrier with a controlled environment within which to house a reticle during storage, transport, processing and shipping. According to a primary embodiment of the present invention, the reticle/mask carrier is equipped with means to control the ingress and build-up of particulate and gas-phase contaminants into the controlled environment. 
         [0014]    The present invention provides systems, components, and processes for providing and maintaining a controlled environment within pods, within pods with bottom opening doors, particularly reticle SMIF pods. 
         [0015]    In an embodiment, a pod has a flexible nozzle-receiving flange positioned on a lower surface of the door of a bottom-opening pod. The nozzle-receiving seal includes a downwardly facing, generally circular, sealing flange that may deflect axially or bend upon loading by a nozzle to form a seal. 
         [0016]    Embodiments of the present invention provide a receiver for removably receiving a bottom-opening pod. In preferred embodiments the receiver is configured as a tray with nozzle interfaces for purging connections with the bottom-opening pod. In certain embodiments, the pod receiver has an aperture sized and positioned for allowing downward venting through a central exit filter on the bottom of a pod. 
         [0017]    In certain embodiments, the bottom-opening pod has a pair of downwardly facing sealing flanges that directly interface with the nozzles on the tray. The sealing flanges support a portion of the weight of the pod and contents. The weight of the pod and contents loads and deflects the sealing flanges, thereby improving sealing contact between the sealing flanges and the nozzles. In an embodiment, the sealing flanges are combined with or integral with an elastomeric and/or resilient bushing or grommet that is received in an aperture extending through the door thus comprising a purge port assembly. The bushing has a bore therein that may receive a check valve component. 
         [0018]    In certain embodiments, a diffuser portion, as part of a grommet, extends above the top surface of the door of the bottom-opening pod. The diffuser has outlets preferably oriented outwardly, so as to direct purge gas away from the patterned surface and pellicle. 
         [0019]    In certain embodiments, the sealing integrity of the purging interfaces between the tray and the pod door can be affected by the positioning and/or stability of the pod on the tray. In an embodiment, the interface between the pod door and tray will be at discrete contact regions on the tray, providing substantially three-point or three regions of contact between the pod and the tray. There may be visually discernable vertical movement upon manual contact with the pod, in that there is preferably a tolerance of at least about 0.1 inch vertically in the resilient engagement of the purge nozzle with the sealing flanges. 
         [0020]    In certain embodiments a purging station provides a plurality of trays arranged in a stacked configuration for receiving the bottom-opening pods. The trays can be movable, for example swivelable in a horizontal direction to provide easy access to the bottom opening pods thereon. 
         [0021]    According to another aspect, the opening in the tray corresponds and is substantially concentric with the filter on the door of the bottom-opening pod. Moreover the filter is preferably shaped and sized substantially proportionate to the reticle and preferably positioned substantially concentrically with respect to the reticle. 
         [0022]    According to yet another embodiment of the present invention, the bottom opening pod is provided with a means to continually inject pressurized, extremely clean dry air, denominated XCDA, into the hermetically sealed space of the reticle carrier and a means to exhaust the XCDA from the sealed space. A continuous purging in the hermetically sealed space in this manner serves to flush out contaminants and prevent haze formation or crazing on the mask/reticle therein. In preferred embodiments, a stack of swivelable trays will have purge lines to provide continuous purging of stored bottom-opening reticle pods. 
         [0023]    Also it is noted that there appear to be similar hazing and contamination issued associated with wafer containers as described above. Thus, aspects of solutions, as described below, are also applicable to wafer containers Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a bottom perspective view of an assembly of a bottom-opening substrate carrier according to a primary embodiment of the present invention; 
           [0025]      FIG. 2  is an exploded perspective view of the assembly of the substrate carrier of  FIG. 1 ; 
           [0026]      FIG. 3  is a perspective view of a base portion or door of the reticle carrier of  FIG. 1  shown supporting a reticle; 
           [0027]      FIG. 4  is a side cross-sectional view through the base portion including a diffuser nozzle assembly in the interior of the pod and further depicted with the pod positioned over a purge tray; 
           [0028]      FIG. 4   a  is a side cross-sectional view through the base portion as depicted in  FIG. 4 , but with the sealing flanges of the diffuser nozzle assembly engaged with the purge nozzle of the purge tray; 
           [0029]      FIG. 5  is a detailed perspective view depicting the components of a diffuser nozzle assembly according to an embodiment of the invention; 
           [0030]      FIG. 6  is a detailed perspective view depicting the components of a diffuser nozzle assembly according to an embodiment of the invention along with a check valve assembly; 
           [0031]      FIG. 7  is a perspective view of a pod library comprising a stack of swivelable trays for receiving bottom opening pods with purging capabilities in accord with the invention herein; 
           [0032]      FIG. 8  is a perspective view of the top side of a tray of the pod library of  FIG. 7 ; and 
           [0033]      FIG. 9  is a bottom perspective view of a tray of the pod library of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    The accompanying figures depict embodiments of a bottom opening pod for holding substrates, specifically configured as a reticle carrier, and a purging station configured as a swivelable stack of trays providing a library of reticle pods. Any references to front and back, right and left, top and bottom, upper and lower, and horizontal and vertical are intended for convenience of description, not to limit the present invention or its components to any one positional or spatial orientation. “Substrate” when used herein refers to wafers, or reticles used in the manufacturing of semiconductors. Any dimensions specified in the attached Figures and this specification may vary with a potential design and the intended use of an embodiment of the invention without departing from the scope of the invention. 
         [0035]    In  FIGS. 1-4   a , there is depicted a bottom-opening pod for substrates configured as a reticle carrier  100  equipped with purge capabilities according to a primary embodiment of the present invention. The reticle carrier  100  (alternatively referred to as a reticle container, a reticle pod, or a reticle box) generally comprises a door portion  106  (alternatively referred to as a base portion) which mates with a carrier shell  112  (alternatively referred to as a cover) to form an hermetically sealed interior space  118  which provides a sealed environment in which a reticle  124  may be stored and transferred. The term “reticle” in used in a broad sense to include quartz blanks, photo-masks, masks used in the semiconductor industry that are susceptible to damage from particulates and gas-phase chemical contaminants. Generally, the reticle  124  is square shaped with a first surface  126  opposite a second patterned surface  128  having a surface area  129  provided with the etched pattern as discussed above. A reticle lateral surface  130  separates the first surface  126  from the second patterned surface  128  and extends around a reticle perimeter  130 . It will be appreciated that the present invention is not limited by a particular shape of reticle  124 . 
         [0036]    The door portion  106 , depicted in  FIGS. 1-4   a  includes an opposed upper door surface  136  and a lower door surface  142  separated by a lateral wall  148 . A plurality of reticle supports  154 , reticle side positioning members  160  and back positioning members  166  extend outwardly from and are disposed in spaced apart relationship adjacent an upper periphery  172  of and generally about a central portion  178  of the upper door surface  136 . The reticle supports  154  are configured to hold the reticle  124  at a predefined height  156  above upper door surface  136 . The reticle side positioning members  160  and the back positioning members  166  serve to guide manual positioning of the reticle  124  and ensure proper lateral and rearward placement of the reticle on the reticle supports  154  so that the reticle substantially occupies and its volume bounded by a reticle receiving region  168  associated with the door portion  106  and defined by the reticle supports  154 , the reticle side positioning members  160  and the back positioning members  166  as best depicted in  FIG. 3 . A Gasket  184  loops along the upper periphery  172  on the door surface  136 . Preferably, the door portion  106  and the carrier shell  112  conform to the shape of substrate including the reticle  124 . 
         [0037]    Referring now to  FIGS. 2 and 3 , door portion  106  includes central hole  190  extending through the door portion  106  and defined by a first opening  196  on the upper door surface  136 , a second opening  202  on the lower door surface  142  and an inside peripheral wall  208  communicating the first opening  196  with the second opening  202 . In an exemplary embodiment, illustrated in  FIGS. 2-3 , the first and second openings  196  and  202  are substantially square shaped and are characterized by their respective first and second areas  212  and  214 . The inside peripheral wall  208  extends generally parallel to the lateral wall  148  of the door portion  106  between the first and the second openings  196  and  202 . The inside peripheral wall  208  is configured with a peripheral shelf  220  suitable for securely supporting a filter frame  226  such that the filter frame  226  is substantially perpendicular to the first opening  196  and is located generally flush with the upper door surface  136 . 
         [0038]    In an embodiment depicted in  FIG. 2 , filter frame  226  can be a semi-rigid, molded plastic receptacle in which a filter  232  in accordance with the present invention may be used. The filter frame  226  is substantially hat shaped with a peripheral flange  242  (alternatively identified as a lip) circumjacent an open end  248 , a filter frame side wall  258  depending from the open end  248  and terminating at a closed end  252  to define a cavity  262  adapted to receive the filter  232 . Closed end  252  has a structure defining a plurality of perforations  264 . Filter frame side wall  258  includes a shoulder  268  with a shape complementary to the peripheral shelf  220  on inside peripheral wall  208 . The filter frame is configured to be inserted through first opening  196  on upper door surface  136  and snug-fittingly received into central hole  190  for detachable mounting in door portion  106  with flange  242  resting on upper door surface  136  and shoulder  268  securely positioned on peripheral shelf  220  of inside peripheral wall  208 . In alternate embodiments, an elastomeric seal or gasket such as for example, the gasket  184  described above, can be interposed between the shoulder  268  and the peripheral shelf  220  to provide a hermetic seal between the filter frame  226  and the filter  232 . 
         [0039]    In an embodiment of the present invention, the first area  212  of the first opening  196  is configured to be substantially proportional to the surface area  129  of the second patterned surface  128  of the reticle  124 . According to one aspect of the particular embodiment, the first area  212  is at least 50% of the surface area and in a further embodiment the surface area is at least sixty percent (60%) of the surface area  129  and preferably in the range of seventy-five percent (75%) to one hundred percent (100%) of the surface area  129 . In the preferred embodiment of the present invention, the first area  212  is substantially concentric with reticle receiving region  168 . Furthermore, the first opening  196  and the location of reticle supports  154  are arranged so that in a assembled configuration, i.e. when the carrier shell  112  is mated to the door portion  106  and the reticle  124  is supported on the reticle supports  154 , the filter  232  is located with the surface area  288  disposed opposite at least a portion of second patterned surface  128  within the hermetically sealed space  118  such that reticle perimeter  130  overlies perimeter  289  of surface area  288 . 
         [0040]    One of skill in the art will recognize that other operative configurations of surface area  288  and second patterned surface  128  are possible without departing from the scope of the present invention. All of the aforementioned operative configurations are selected to maximize the extent of the surface area  288  relative to the second patterned surface  128  based in part upon the dimensions of the hermetically sealed space  118 , the diffusion length generated during reticle carrier purging, reticle processing, transport, shipping and storage and other conditions the reticle  124  might encounter during its residency within the reticle carrier  100 . The surface area  288  is disposed proximate the second patterned surface  128 . By selecting the extent and location of surface area  288  in the manner of the present invention, the probability, that a particulate present within or entering the hermetically sealed space  118  will preferentially encounter and settle upon the surface  288  instead of diffusing onto the secondary patterned surface  128 , is maximized. To those skilled in the art, the extent of surface area  288  is representative of the total number of fluid passages available for entry of a fluid into the filter  232 . The term “high-surface area” associated with reference numeral  338 , on the other hand, refers to the effective surface area of the total filter media available for filtration as the fluid flows through the entire thickness  290  of the filter  232 . The effective surface area controls adsorption of gases and chemical reactions. In this regard, the filter  232  differs from the prior art SMIF pod filters in that the filter  232  of the present invention is structurally a significant component of the door portion  106  because surface  288  can extend over a substantial portion of the upper door surface  136 . Furthermore, in the assembled configuration, base layer  276  is positioned on closed end  252  so that filter  232  places the hermetically sealed space  118  in fluid communication with the ambient atmosphere outside the reticle pod  100  through the plurality of perforations  264 . 
         [0041]    According to an embodiment of the present invention, the concentration of moisture within the hermetically sealed space  118  is preferably maintained at concentration levels approaching a few parts per billion (ppb). Using prior art approaches, such as dessicants for example, moisture concentrations within the hermetically sealed space  118  can be controlled only to within a few parts per million (ppm). The level of humidity control achieved by coupling reticle pod  100  to a purging system which periodically flows a very dry gas, such as for example dry nitrogen gas or dry argon, through the hermetically sealed space  118 . 
         [0042]    One of skill in the art will recognize that injecting a very dry purge gas, for example dry nitrogen gas and dry argon gas, under pressure into the hermetically sealed space  118  will cause at least a portion of the purge gas to egress through the filter  232  and out into the ambient atmosphere through the closed end  252 . An apparatus and method of purging the reticle carrier  100  is described in U.S. Pat. No. 5,988,233 and U.S. Pat. No. 5,810,062, the entire contents of the two patents being incorporated herein by reference in their entirety. In an alternate embodiment, the hermetically sealed space  118  is pressurized by the purge gas flowing into it through purge diffuser fittings. The purge gas exits the hermetically sealed space  118  through the filter  232 . Generally, purging the hermetically sealed space  118  removes trace contaminants by entraining them in the gas flow. Purging with dry gas also dehumidifies the filter  232 . Purging under pressure may dislodge and thus remove particulates and other contaminants that may be weakly bonded to the physisorptive media filter elements and the filter elements that specifically filter particulates. In effect, purging regenerates filter  232  by replenishing its capacity to adsorb contaminants. One of skill in the art will appreciate that the capacity of the filter  232  of the present invention may also be replenished by replacing the depleted filter  232 . 
         [0043]    According to an embodiment depicted in  FIGS. 2 ,  4 ,  4   a ,  5 , and  6 , the nozzle interface or purge port assembly  350  generally includes diffuser body portion  352 , nozzle receiving portion  354 , and optionally, check valve assembly  356  and filter  357 . Body portion  352  generally includes barrel portion  358 , defining lateral channel-shaped groove  360 , and upper spherical portion  362 . Diffuser body  352  defines hollow interior space  364 . A plurality of diffuser ports  366  are defined on one side of upper spherical portion  362 , and extend through from hollow interior space  364 , configured as a bore, to exterior surface  368 . Nozzle receiving portion  354  generally includes shank or tubular portion  370  with integral resiliently flexible sealing flange portion  372  at lower end  374 . Shank portion  370 , configured as a tubular portion, defining hollow interior space  376 . Inlet opening or aperture  378  extends through flange portion  372  to interior space  376 . Flange portion  372  includes a supported flange portion  381  adjacent and integral with the tubular portion  370  and a cantilevered flange portion  383  integral, concentric, and radially outward from the supported flange portion  381 . The supported portion  372  has a diameter of d 1 , suitably ¼inch to ¾ of an inch and the cantilevered flange portion has a diameter d 2  of, suitably ⅜ inch to 1 inch. 
         [0044]    The diffuser body portion and nozzle receiving portion are formed of a resilient polymer such as Hytrel® (a polymer of E.I. DuPont de Nemours and Company). Other thermoplastics, such as PBT (polybutylene terephthalate) may be suitable, including elastomers. 
         [0045]    As depicted in  FIG. 2 , door portion  106  defines apertures  400 ,  402 , extending through from upper door surface  136  to lower door surface  142 . Each aperture  400 ,  402 , has inwardly facing circumferential edge  404  Bottom edge  380  of barrel portion  358  may be rounded or beveled to enable insertion of diffuser body  352  into apertures  400 ,  402 , from upper door surface  136 . 
         [0046]    A separate purge port assembly  350  is received through each of apertures  400 ,  402 . Inwardly facing circumferential edge  403  is received in lateral groove  360  to sealingly secure the purge diffuser assembly in place in the aperture. Importantly, diffuser ports  366  are oriented outwardly toward lateral wall  148  so that purge gas is introduced intermediate the sides of the reticle and directed away from the patterned surface or pellicle. As depicted in  FIGS. 4 and 4   a , shank or tubular portion  370  of sealing insert  354  is sealingly received in hollow interior space  364  of diffuser body  352  with flange portion  372  facing downwardly. 
         [0047]    In  FIGS. 7-9  there is depicted an embodiment of a purging station  500  including a plurality of purging trays  502  arranged in a stacked configuration and swivelable in a horizontal direction about central column  504  to provide easy access to the bottom opening pods  100  thereon. An enclosure  503  may be provided to provide containment of the station. Each tray  502  generally includes a planar deck portion  506  defining a recess portion  507  defining a substrate container or reticle pod, receiving region  509  and a central aperture  508 , corresponding with filter frame  226  of pod  100 . A pair of purge nozzles  510  extend upwardly from tray  502  and are coupled with a source  300 . 1  of very dry purge gas through tubing  512  as depicted in  FIGS. 4 and 4   a . Each purge nozzle  510  has upper peripheral lip  514  and defines a generally bowl shaped recess  516  with inlet port  518 . Lip  514  has a diameter d 3  suitably greater than the diameter d 1  of the supported flange portion and less than the diameter d 2  of the cantilevered flange portion. Tray  502  may further include third pod contact point  520 . 
         [0048]    In use, pod  100  is placed over tray  502  with each of flange portion  372  registered with one of purge nozzles  510  as depicted in  FIG. 4 . As pod  100  is rested on tray  502 , flange portion  372  engage purge nozzles  510  and bend or deflect upwardly as they are loaded by the weight of pod  100  as depicted in  FIG. 4   a  to an angle α. The lower surface  503  of the body portion may provide a curved hard stop to the cantilever flange portion. Third pod contact point  520  may contact a point on lower door surface  142  such that pod  100  is supported on tray  502  only at purge nozzles  510  and third pod contact point  520 . Preferably, with the weight of pod  100  resting on flanges  372 , there may still be a visually discernable vertical movement upon downward force applied to pod  100 , in that there is preferably a tolerance of at least about 0.1 inch vertically in the resilient engagement of the purge nozzles  510  with the flange portion  372  when manual force is applied thereto. 
         [0049]    Dry gas may then be introduced through tubing  512  and will flow through purge nozzles  510  and into purge diffuser assembly  350  through inlet openings  378 . The dry gas will then be directed into the hermetically sealed space  118  through diffuser ports  366 . In that diffuser ports  366  are oriented outwardly away from the reticle, the gas will not impinge on any patterned surface. A portion of the purge gas will egress through the filter  232  and out into the ambient atmosphere through the closed end  252 . 
         [0050]    Each of the purge diffuser assemblies  350  may be equipped with a check valve assembly  356  received in hollow interior space  376  of sealing insert  354 , and configured to allow a unidirectional flow past and prevent ingress or egress of gaseous or particulate contaminants into the hermetically sealed space  118  when the system is not in use. Diaphragm valves with slits such as those described in U.S. Pat. No. 5,482,161 referenced above may also be employed in conjunction with or without the check valve assemblies  356 . This is a mechanical means for limiting the exposure of the filter media  276 ,  278 ,  280 ,  282  and other media that the filter  232  may comprise of, to the ambient atmosphere external to the reticle carrier  100 . 
         [0051]    Of course, many alternative embodiments of the present SMIF reticle pod are possible and are within the scope of the invention, as will be appreciated by those of skill in the art. Moreover, the inventive aspects are applicable to other substrate containers such as FOUPS (front opening unified pods) for storing wafers. Such wafer containers are disclosed in U.S. Pat. Nos. 6,736,268 and RE 38,221, the disclosures of which are incorporated by reference herein. These substrate containers applicable to the invention have interior volumes ranging, preferably from about ⅓ of a liter to 10 liters and are generally principally comprised of rigid polymers such as polycarbonate. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention.