Abstract:
The present invention provides a reticle container that is equipped with a secondary container which houses the reticle and is housed in the primary container. The secondary container is held within the primary container with shock and vibration isolation members so that the secondary container has multiple degrees of freedom of motion within the primary container. The reticle is secured inside the secondary container such that shock and vibration transmission from the reticle container to the reticle is substantially attenuated.

Description:
RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of U.S. Provisional Application Ser. No. 60/657,616, filed Feb. 27, 2005, U.S. Provisional Application Ser. No. 60/657,355, filed Feb. 27, 2005, and U.S. Provisional Application Ser. No. “unknown”, filed Feb. 18, 2006 (Attorney Docket No. 2267.1110US01), which are included herein in their entirety by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to substrate carriers and in particular to processor carriers and shippers and in particular to reticle containers.  
       BACKGROUND OF THE INVENTION  
       [0003]     Photolithography is one of the process steps commonly encountered in the processing of silicon wafers for semiconductor applications. 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. Typically, 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 smaller and 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 mn. 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 thereby 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. Typically, the patterned surface of the reticle is coated with a thin, optically transparent film, typically 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 contaminants migrating to the image plane. However, extreme EUV utilizes reflection from the patterned surface as opposed to transmission through the reticle characteristic of deep ultraviolet light photolithography. Currently, 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 container designed to receive, store, transport and ship a reticle destined for EUV photolithography use.  
         [0006]     Clearly, unnecessary and unintended contact with other surfaces during manufacturing, processing, shipping, handling, transport or storage is highly undesirable in view of the susceptibility of the delicate features on the patterned surface of the reticle to damage due to sliding friction and abrasion. Secondly, any particulate contamination of the surface of the reticle will likely compromise the reticle to a degree sufficient to seriously affect any end product obtained from the use of such a reticle during processing. Particles can be generated within the controlled environment containing the reticle during processing, transport and shipping. Sliding friction and consequent abrasion is one source of contaminating particulates. A reticle sliding from its desired position in a reticle container during transport, for example, is another source of particulates. Such an out-of-position reticle will also likely be misaligned when automatically retrieved from the container and positioned into processing equipment potentially leading to an end product that is of unpredictable quality. Sliding contact during placement and removal of a reticle from the container to the lithography equipment also creates opportunities for particulate generation and contamination. Finally, shock and vibration of the container can be transmitted to the reticle and components holding the reticle causing friction and associated particle generation.  
         [0007]     Conventionally, reticles are shipped to the fabrication facility in which they are used in one container and are stored in the fabrication facility inbetween uses in other containers. The shipping containing is typically discarded after use. The transfer of the reticles from the shipping containers to the containers in which they are stored within the fabrication facility creates another opportunity for contamination. Conventional requirements for shippers for reticles and containers for use within the fabrication facility are dramatically different. Combining the container for both uses would eliminate the opportunity of incursion and generation of particulates during the transfer from the shipper container to the fabrication facility use container but presents significant design challenges. For example the container would need to be able to handle the potential dramatic changes in atmospheric pressure during transportation, such as associated with altitude and temperature changes. Also shock absorption capabilities in transportation are much more demanding than in the controlled robotic transfers occurring in fabrication facilities.  
         [0008]     Some of the considerations discussed above are also applicable to semiconductor wafer substrates. Recognizing the need for a controlled environment around the wafer, especially during storage, processing and transport, 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 to house the wafer so that it can be kept relatively free from incursion of particulate matter.  
         [0009]     Wafers are typically shipped to a fabrication facility in a shipping container and then transferred to a separate container for storing the wafers in between processing steps in the fabrication facility. 200 mm wafers are typically shipped in sealed plastic “shippers” either edge supported in a spaced array or stacked vertically with sheet material spacers in “coin stack wafer shippers” Industry standardized containers for holding 200 mm wafers in between processing steps in fabrication facilities are known as standard mechanical interface pods, or SMIF pods and having bottom opening doors. For 300 mm wafers, the shippers are known as front opening shipping boxes, or FOSBS, and the containers for holding the wafer in between process steps are known as front opening unified pods, or FOUPS. Reticles stored in Fabrication facilities in between fabrication steps now often are stored in bottom opening containers similar to the standardized SMIF pods and are termed reticle SMIP pods, or RSPs.  
         [0010]     Even when substrates, that is wafers and reticles, are in such a controlled environments, particulates that may be present inside the controlled environment can migrate 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, such as by simply opening and closing the container. Also, thin walled shippers or FOSBS 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 can compromise the functioning of the support and retaining mechanisms leading to wafer misalignment and/or warping of the substrate carried within the container. Dimensional changes of the container wall due to pressure fluctuations can compromise the sealing between the cover and the door of the carrier allowing particulate incursion within the carrier.  
         [0011]     Prior art approaches, particularly in wafer containers, utilize 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. A filter interposed in the path is expected to provide a barrier to incursion of particulates from the external environment into the controlled environment of the carrier. However, as noted above, the reticle used in a EUV photolithography process has very fine and delicate features so the critical particle sizes are only of the order of 0.1 μm and 0.03 μm for the non-patterned and patterned surfaces of the reticle respectively. At such low particle sizes, a filter would require a very fine pore size causing a considerable resistance to fluid flow across it thereby necessitating a larger filter surface area. The alternative to a larger filter surface area is a slower response to sudden pressure changes such as those encountered in shipping the container. Both of these are not desirable alternatives because one of the objectives of reticle SMIF pod design is to keep the controlled volume to a minimal so it can be effectively sealed against incursion of particulates. Minimizing the controlled volume within which the reticle is positioned whilst providing for a large filter area to achieve pressure equalization within the controlled volume are incompatible objectives.  
         [0012]     It is desirable that particulates that are generated or are otherwise introduced or present within the controlled environment are prevented from settling on the reticle. In this regard, it is preferable to have a minimal volume for the environment within which the reticle is carried and which has to be controlled to avoid particulate contamination. It is also desirable that the air in the controlled volume remains relatively static. For example, the deflection of a wall of the container in response to large and sudden pressure differences can induce a pressure wave inside the container.  
         [0013]     Reticles come in various sizes, including a  5 ″,  6 ″,  7 ″,  8 ″, 150 mm and 200 mm diameter reticle. However, the SMIF pod door is equipped with features in compliance with currently implemented “SMIF” (Standard Mechanical Interface) pod standards so that the SMIF pod door can be interfaced with automatic reticle handling processing machinery. As the reticle sizes continue to evolve, it becomes increasingly challenging to support a reduced diameter reticle with minimal volume for the environment within which the reticle is carried if the SMIF pod is a legacy SMIF pod designed for an earlier generation, larger sized reticle. In this respect it would be advantageous to be able to use a legacy SMIF pod but support a reduced diameter reticle that the pod was not originally designed for.  
         [0014]     What is needed is a substrate container suitable for use both as a shipper and to store the substrates in between processing steps in the fabrication facilities. What is needed is a container that provides improved shock absorption capabilities during transportation. What is needed is a container that provides improved resistance to particulate generation and minimization of particle disruption or movement within a substrate container during transportation, and opening and closing of the container.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention is directed to an apparatus for supporting a substrate to provide shock and vibration isolation, the apparatus comprises an outer primary pod, comprising a cover and a base preferably configured as a bottom opening door, and a secondary pod supported therein by resilient shock and vibration isolation members. Cover and base of the primary pod are configured to be mated to provide a hermetically sealed first enclosure The secondary pod is desirably supported exclusively by elastomeric members extending both from the cover and the base. In preferred embodiments the secondary pod has multiple degress of freedom of motion, preferably six, with respect to the primary pod and moves with the reticle contained therein in isolation from the outer primary pod. The actual motion allowed may be minimal, but is sufficient for absorbing a portion of the energy from shocks imparted to the primary pod. The secondary pod is configured with a lower portion configured as a tray having a reticle support structure, preferably corner posts having lateral restraints and a elastomeric pad upon which the reticle seats. An upper portion of the tray engages with the lower portion to define the secondary enclosure and also preferably has elastomeric pads to engage the top surface of the reticle. The upper and lower portion may provide a hermetic seal such as by an elastomeric member or other sealing means such as hard planar surface to hard planar surface contact or may have a restricted opening, an elongate gap extending substantially around the periphery of the secondary pod to minimize pressure shock waves and inhibit particles without a hermetic seal.  
         [0016]     Additionally, the cover of the primary pod may be supported by elastomeric seal to provide shock absorption with respect to the top cover and the base. In a preferred embodiment the elastomeric seal may have two cantilevered portions and a central spanning portion and be positioned within groove in upwardly facing surface of the base for engagement with downwardly extending ribs integral with the top cover.  
         [0017]     The inner secondary pod can be replaced utilizing the same essential configuration of the primary pod with a upper portion and lower portion configured to secure a different size reticle therein.  
         [0018]     It is a feature and advantage of preferred embodiments of the invention to provide enhanced shock and vibration isolation to the reticle.  
         [0019]     It is a feature and advantage of preferred embodiments of the invention to provide enhanced shock and vibration absorption before such shock and vibration reaches the reticle contained therein.  
         [0020]     It is a feature and advantage of preferred embodiments of the invention to provide a dual containment to the reticle with is particularly advantageous for utilizing the pod as both a shipping device and a device for storing the reticle within the fabrication facility particularly intermediate processing steps.  
         [0021]     It is a feature and advantage of preferred embodiments of the invention to provide a reticle SMIF pod that may be used to transport and store different sizes of reticles using a common size, namely 200 mm.  
         [0022]     It is a feature and advantage of preferred embodiments of the invention to provide a reticle SMIF pod that is particularly suitable for use with EUV lithography techniques.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a cross-sectional elevational view of an assembled container according to one embodiment of the present invention.  
         [0024]      FIG. 2  is an exploded perspective view of an assembly of the container according to an exemplary embodiment of the present invention.  
         [0025]      FIG. 3  is an exploded cross-sectional elevational view of an assembly of the container including the components of the isolation system according to the primary embodiment of the present invention.  
         [0026]      FIG. 4  is a perspective view of a cover according to a primary embodiment of the present invention.  
         [0027]      FIG. 5  is a perspective view of a base and a substrate supported on the base according to the primary embodiment of the present invention.  
         [0028]      FIG. 6  is a perspective view looking upward of the cover and components of a secondary pod according to an exemplary embodiment of the present invention.  
         [0029]      FIG. 7A  is a cross-sectional side view of an assembled container according to an alternate embodiment of the present invention.  
         [0030]      FIG. 7B  is a perspective sectional view of an assembled container according to an embodiment of the present invention.  
         [0031]      FIG. 8A  is a detailed cross-sectional view illustrating an engagement between the cover and the base according to an alternate embodiment of the present invention.  
         [0032]      FIG. 8B  is a detailed cross-sectional view illustrating an engagement between the cover and the base showing the cover contacting the base according to the primary embodiment of the present invention.  
         [0033]      FIG. 9A  is an illustration of an exemplary seal in an undeformed configuration according to the present invention.  
         [0034]      FIG. 9B  is an illustration of a deformed configuration of the exemplary seal of  FIG. 9A .  
         [0035]      FIG. 10A  is a top view of the lower portion (or tray) according to an exemplary embodiment of the present invention.  
         [0036]      FIG. 10B  is a side sectional view of the lower portion (or tray) of  FIG. 10A .  
         [0037]      FIG. 10C  is a top perspective view of the lower portion (or tray) according to an exemplary embodiment of the present invention.  
         [0038]      FIG. 10D  is a detailed view of a support structure for holding the substrate on the lower portion (or tray) illustrated in  FIG. 10A-10D .  
         [0039]      FIG. 11  is a schematic illustrating an exemplary shock and vibration isolation system according to the present invention.  
         [0040]      FIG. 12  is a schematic illustrating a shock and vibration isolation system according to the primary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     References to relative terms such as upper and lower, front and back, left and right, or the like, are intended for convenience of description and are not contemplated to limit the present invention, or its components, to any one positional or special orientation. All dimensions depicted in the figures may vary with a potential design and the intended use of a specific embodiment of this invention without departing from the scope thereof.  
         [0042]     Each of the additional figures and methods disclosed herein may be used separately, or in conjunction with other features and methods, to provide improved containers and methods for making and using the same. Therefore, combinations of features and methods disclosed herein may not be necessary to practice the invention in its broadest sense and are instead disclosed merely to particularly describe representative and preferred embodiments of the instant invention.  
         [0043]     Referring now to  FIG. 1 , there is illustrated a reticle container  10  (alternatively identified as a reticle “pod” or reticle “carrier” or “primary pod”) according to a primary embodiment of the present invention. The reticle container  10  generally includes a cover  15  capable of sealingly mating with a base  20  (alternatively identified as a door) to define a hermetically sealed enclosure  25  within the container  10  for containing a reticle  30  during storage, transport, processing and shipping. Reticle  30  thus located within sealed enclosure  25  is effectively isolated from particulate contaminants external to the enclosure  25 . As best explained with reference to  FIG. 3 , the container  10  generally includes a reticle support structure  32  and a reticle retaining structure  34  mounted on the base  20  and on the cover  15  respectively within the sealed enclosure  25 . The reticle  30  is located and supported on the reticle support structure  32  mounted to the base  20 . Upon engaging the cover  15  with the base  20 , the reticle retaining structure  34  mounted on the cover  15  operates to secure the reticle  30  on the reticle support structure  32  as best seen in the illustration of  FIG. 1 . Reticle support structure  32  defines a lower portion  35  and reticle retaining structure  34  defines an upper portion  37  of secondary pod  39  having an interior  41 .  
         [0044]     Referring now to  FIGS. 1, 2  and  3 , the base  20  is provided with features to comply with Semiconductor Equipment and Materials International (SEMI) standards for automated use with various types of wafer-fabrication equipment. In an exemplary embodiment, the base  20  is at least partially compliant with similar bases on Reticle “SMIF” (Standard Mechanical Interface) pods used with microlithography systems well-known in the art. In the exemplary embodiment illustrated in  FIGS. 2 and 5 , the base  20  has a base lower-surface  21  bounded by a base peripheral edge  35  and having footprint of area (not illustrated) opposite a base upper-surface  40  spaced from the lower surface by a base lateral surface  42  comprising the door enclosure wall. The base lower surface is provided with features in accordance with SMIF standards so as to be compatible with semiconductor processing equipment (not shown). The SMIF compliant base  20  is also adapted to be removably coupled to the cover  15  by means of a door-latch mechanism  23  capable of being opened by a SEMI conformable latch opening device (not illustrated). An exemplary latching-mechanism is disclosed in U.S. Pat. No. 4,995,430 owned by the owner of the instant application and incorporated herein by reference. The cover  15  is generally equipped with an automation flange  45  configured for interfacing with a process tool (not illustrated) as well as for manual grasping during transport, storage or shipping of the container  10 . In the illustrated embodiments of  FIGS. 1, 2  and  3  the cover  15  and the base  20  are shown to be generally rectangular to conform to the shape of the reticle  30 . However, one of skill in the art will readily recognize that the cover and the base could have other shapes without departing from the scope of the present invention.  
         [0045]     Container elements, exemplified, for example, by the cover  15  and the base  20 , are preferably formed of a rigid thermoplastic polymers, by a process of injection molding or other suitable mariufacturing process. The polymer can be clear to allow the viewing of the reticle  30 . The container elements may additionally be static dissipative. An example of such a transparent, static dissipative material, is polymethyl methacrylate. The container elements may alternatively be formed of static dissipative, carbon fiber-filled polycarbonate, which is opaque, and configured to include transparent window(s) (not illustrated), through which the reticle may be viewed. As a further alternative, the container elements may be formed of clear polycarbonate. As an alternative to polycarbonate, the elements may further be formed of flame retardant polyetherimide. It is understood that the container elements may be formed of other materials in alternative embodiments. The container elements are preferably formed by injection molding, but other known methods of manufacture are also contemplated. An exemplary reticle SMIF pod is described in U.S. Pat. No. 6,216,873 to Asyst Technologies Inc., the contents of which are incorporated herein by reference. Use of reticle pods in EUV applications is described in detail in U.S. Pat. No. 6,906,783, which is incorporated herein by reference.  
         [0046]      FIG. 2  depicts an exemplary reticle  30  according to the present invention. As seen in FIGS.  2  the reticle  30  is generally square shaped with a first patterned surface  50  opposite a second chucking surface  55  and spaced apart by a lateral surface  60 . The first patterned surface  50  intersects the lateral surface  60  at first and second lower pair of parallel edges  65  and  70  respectively. The second chucking surface  55  intersects lateral surface  60  at first and second upper pair of parallel edges  75  and  80  respectively. In a typical rectangular shaped reticle illustrated in  FIG. 2 , first and second lower pair of edges  65  and  70  are parallel to respective first and second upper pair of edges  75  and  80 , each corresponding pair of parallel edges of a surface blends with the other corresponding pair of parallel edges at radiused corners  85 . The patterned surface  50  is etched with the desired circuit pattern (not illustrated). The chucking surface  55  may be used as a reference surface during the manufacture and handling of the reticle. For example, the chucking surface  55  may be held in an electrostatic chuck. The very fine features on the patterned surface  55  can be easily damaged upon contact with other surfaces, such as the surfaces of the container  10 . To avoid such contact, the reticle  30  is generally supported at peripheral portions of the reticle surfaces  50  and  55  that are proximate the radiused corners  85  because these portions are typically pattern free. Likewise, the reticle  30  may also be contacted along its edges without damaging it. But contacting surfaces must be restrained against motion relative to each other because of the potential for generating particulates by abrasion of the contacting surfaces. Positional locators and other structural features may be incorporated on the cover  15  to allow for mating the cover and door without having to adjust for misalignment between cover and door thereby reducing reticle sliding friction. The present invention is described with reference to a square shaped reticle but one of skill in the art will appreciate that reticles of all shapes are within the scope of the present invention including. Reticles may be, but are not limited to, polygonal or rectangular in shape.  
         [0047]     As best seen in the illustrations of  FIGS. 4 and 6 , the cover  15  includes a canopy  90 , cover side walls  95 . and cover engagement surface  100 . Canopy  90  comprises a canopy peripheral edge  105 , a canopy concave inner surface  110  opposite a canopy exterior surface  115 . Cover engagement surface  100  extends between and is located circumjacent canopy peripheral edge  105  and cover side walls  95 . Upon engaging cover  15  with base  20 , base upper surface  40  is positioned facing cover engagement surface  100  with the cover side walls  95  located circumjacent base lateral surface  42  so that the base  100  is substantially disposed within canopy  90 . In this configuration, canopy concave inner surface  110  in conjunction with base upper surface  40  together form sealed enclosure  25  as will be detailed below. In the exemplary embodiment illustrated in  FIGS. 4 and 6 , canopy  90  further comprises a structure defining a vent  120 . The vent  120  serves to communicate the sealed enclosure  25  within the container  10  to the ambient atmosphere exterior to the container  10  when cover  15  is mated with base  20 . A flexible diaphragm  125 , shown in  FIG. 5 , is sealingly attached to canopy  90  and configured to extend over vent  115  to prevent sealed enclosure  25  from communicating with the ambient atmosphere through the vent  115 . A change in pressure, without or within the sealed enclosure  25  is desirably equilibriated by a movement of the diaphragm. The automation flange  45  is attached to the canopy  90  on the exterior surface  115  and is configured with an apertured dome shaped portion  128  that extends over the diaphragm  125  so as to shield the diaphragm  125  from external contact while allowing exposure to the ambient atmosphere.  
         [0048]     In the primary embodiment illustrated in  FIGS. 2, 5 ,  10 A,  10 B,  10 C and  10 D, the reticle support structure comprises a plurality of resilient couplings preferably formed of elastomeric material, preferably a thermoplastic elastomer, configured as reticle support posts  130  and a reticle support frame  135  (alternatively identified as a lower tray or lower portion of a secondary pod). Alternative cushioning material may be utilized. Reticle support posts  130  are mounted to or formed on base  20  and configured to extend outwardly from the upper surface  40  to terminate at support post ends  140 . An exemplary embodiment of the reticle support frame  135  comprises a substantially square plate  140  with a support frame upper surface  145  and opposed support frame lower surface  150  extending between support frame corners  155  and support frame edges  160 . Support frame upper surface  145  is spaced apart from support frame lower surface  150  by support frame variable thickness  165  so that support frame plate edges  160  present an arcuately profiled cross-section  170 . Each of the support frame corners  155  is provided with a first support frame gusset  170  and a second support frame gusset  175  formed on the support frame lower surface  150  with the first and second support frame gussets  170  and  175  extending inwardly toward an support frame opposite corner  155  and inwardly toward an opposite support frame corner respectively. Reticle support posts  130  are attachable at support post ends  140  to support frame lower surface  150  proximate each of the corners  155 . Each support frame corner  155 , opposite the point of attachment of resilient support posts  130 , is provided with a reticle support pad  180  extending outward from the support frame upper surface  145  to present a beveled concavity  185  removed from the support frame upper surface  145 . Beveled concavity  185  includes a pair of beveled concavity sidewalls  190  and  195  which are sloped generally downward the reticle support plate  135  and which form right angles with each other in a plane normal to lateral surface  60  of the reticle  30 . Included in between the two beveled concavity sidewalls  190  and  195  and substantially equidistant from them is a dome shaped protrusion  200  extending from first support frame upper surface  145  proximate support frame corners  155 . The sloping sidewalls  190  and  195  of each beveled concavity  185  support the reticle  30  by contacting the reticle  30  at first and second lower pair of parallel edges  65  and  70  proximate radiused corners  85 . The reticle  30  contacts the dome shaped protrusion  200  over a minimal contact area thereby effectively minimizing the overall contact of the reticle  30  with the container  10 . In an alternate embodiment illustrated in  FIG. 7A , dome shaped protrusion is sized to separate reticle  30  from support frame upper surface  145  to create a diffusion layer  210  that restricts fluid flow over the patterned surface  50  to prevent particulates from being transported to the patterned surface  50 .  
         [0049]     Still referring to  FIGS. 2, 3 ,  5 ,  6 ,  10 A,  10 B,  10 C and  10 D, the reticle retainer structure comprises a plurality of reticle retainer posts  230  and a reticle retainer frame  235  (alternatively identified as a upper tray or upper portion of a secondary pod). Resilient couplings formed preferably of elastomeric material, preferably a thermoplastic elastomer, are configured as reticle retainer posts  230  and are mounted to or formed on cover  15  and configured to extend outwardly from the canopy concave inner surface  110  to terminate at retainer post ends  240 . An exemplary embodiment of the reticle retainer frame  235  comprises a substantially square plate  240  with a retainer frame upper surface  245  and opposed retainer frame lower surface  250  extending between retainer frame corners  255  and retainer frame edges  260 . Each of the retainer frame corners  255  is provided with a first retainer frame gusset  270  and a second retainer frame gusset  275  formed on the retainer frame lower surface  250  with the first and second retainer frame gussets  270  and  275  extending inwardly toward an retainer frame opposite corner  255  and inwardly toward an opposite retainer frame corner respectively. Reticle retainer posts  230  are attachable at retainer post ends  240  to retainer frame lower surface  250  proximate each of the corners  255 . Each retainer frame corner  255 , opposite the point of attachment of resilient retainer posts  230 , is provided a dome shaped retainer protrusion  300  extending from retainer frame upper surface  245  proximate retainer frame corners  255 . Upon engaging the cover  15  with the base  20 , reticle support frame  135  and reticle retainer frame  235  engage each other to form a secondary pod  300  circumscribing a secondary enclosure  310  containing the reticle  30 . In this configuration, dome shaped retainer protrusions  301  contact reticle upper surface  55  proximate corners  85  to secure the reticle  30  against movement relative to the secondary pod  300 . Centering fins  302  or guide gussets can help center the reticle or aid in correct positioning of the upper portion on the lower portion. The reticle  30  is supported in a plane substantially normal to the lateral surface  60  on spaced apart reticle support pad  180  after self-centering itself on beveled concavity sidewalls  190  and  195  with the patterned surface  50  resting on dome shaped protrusions  200  and with the dome shaped retainer protrusions  300  bearing down on the chucking surface  55 . Both, the reticle support posts  130  and the reticle retainer posts  230  are adapted to have low stiffness in an axial (z-direction) and lateral, i.e. in the x- and/or y-direction, so as to deform and deflect in response to any shock and vibration loading in those directions. Reticle retainer posts  230  are adapted to cooperate with reticle support posts  130 , dome shaped protrusion  200  and dome shaped retainer protrusion  300  so that when cover  15  is mated with base  20 , the reticle retainer posts  230  and reticle support posts  130  deform in the z-direction to maintain a continuous bias on surfaces  50  and  55  of reticle  30  with the dome shaped protrusions  200  and  300  applying local pressure sufficient to retain the reticle  30  in a desired, fixed reference position sandwiched between the reticle support structure  32  and the reticle retainer structure  34  during storage and transport. The domed shaped protrusions  200  and dome shaped retainer protrusions  300  may be formed of an elastomeric material to provide a high friction cushioning engagement with the surfaces  50  and  55  of reticle  30 . One of skill in the art will appreciate that the arrangement of reticle support posts  130  and reticle retainer posts  230  will reduce the effect of vibration of the mounting base  20 , i.e. the door and/or the cover  15 , on the reticle  30  as will be clear from the schematic illustrations in  FIGS. 11 and 12 .  
         [0050]     Referring to  FIGS. 1, 2 ,  3  and  12 , the resilient couplings  130  and  230  effectively suspend the secondary pod  300  within the primary pod  10 , that is, the secondary pod is structurally connected to the primary pod entirely or exclusively through the elastomeric material comprising the resilient couplings. Said resilient couplings may be tubular shaped with axial bores  231  for easy assembly onto posts  232  on the upper portion, posts one the lower portion  233  of the secondary pod as well as posts  236  on the cover and posts  237  on the base of the primary pod.  
         [0051]      FIGS. 11 and 12  are an idealized schematic representation of the primary pod  10  supporting the secondary pod  300  containing the reticle  30 . As can be seen in the illustrations of  FIGS. 11 and 12 , reticle support posts  130  and reticle retainer posts  230  behave like spring-damper vibration isolation elements that allow the secondary  300  (and the reticle  30  contained therein) to be supported within the primary pod  10  with six degrees of freedom of motion. One of skill in the art will readily recognize that the arrangement of  FIGS. 11 and 12  will substantially attenuate transmission of any shock and vibration loading of the primary pod  10  to the secondary pod  300 . Reticle support frame  130  and reticle retainer frame  230  may be formed of a substantially rigid, electrostatically dissipative, non-particulating material such as for example carbon fiber-filled polyetheretherkeytone (“PEEK”). When the reticle container  10  encounters vibration or shock loading tending to deflect the resilient support posts  130  and the resilient retainer posts  230 , the rigid reticle support frame  135  and reticle retainer frame  235  move as a substantially rigid body acting to constrain the deflections of the support posts  130  and retainer posts  230  and providing mass damping so that the reticle  30  is always maintained in the desired configuration within the container  10 . In an alternate embodiment, reticle retainer frame  235  mates with reticle support frame  135  to form a secondary enclosure  310  (shroud of protection) within primary hermetically sealed enclosure  25  as best illustrated in  FIGS. 1 and 7 A. Secondary enclosure  310  is in fluid communication with hermetically sealed enclosure  25  but the air contained within the secondary enclosure  310  is relatively less susceptible to turbulence because of the smaller volume of air involved and the tortuous fluid flow path between the primary enclosure  25  and the secondary enclosure  310  created by the shroud of protection.  
         [0052]     Another feature of the isolation system of the present invention is best described with reference to  FIGS. 7A, 7B ,  8 A,  8 B,  9 A and  9 B. Base upper surface  40  is provided with a structure defining a plurality of concentric ridges  400  that each define a peak  405  and a valley  410  extending in a loop on base upper surface  40  circumjacent base lateral surface  42  and radially outboard of the secondary pod  300 . An elastomeric seal  415  is provided configured in a loop. The elastomeric seal  415  comprises opposed first and second seal major surfaces  420  and  425  extending laterally between inner and outer peripheral edges  430  and  435  of the seal and forming a continuous loop. The second major seal surface  420  is configured with a plurality of concentric, spaced apart wedges  440  (alternately referenced as “fingers”, protrusions, projections, tongue shaped projections) extending outwardly from the second major seal surface  425 , the wedges  440  are sized to be snug-fittingly received and held within consecutive valleys  410  of the concentric ridges  400  on base upper surface  40 . Lateral portion  445  and  450  on each side of the concentric ridges  400  cantilever over the upper base surface  40 . The cover engagement surface  100  is provided with a plurality ribs  455  complementary to the valleys  410  and dimensioned to bear down upon the first major seal surface  420  of the elastomeric seal  415  and substantially proximate the wedges  440  so as to compress the wedges  440  into sealing contact within the valleys  410  upon mating the cover  15  with the base  20  to form the hermetically sealed enclosure  25 .  
         [0053]     In an exemplary embodiment shown in  FIGS. 9A and 9B , the elastomeric seal  415  deforms to take a shape substantially like the Greek letter Π. In the undeformed state, the horizontal bar of the Π is arched like an inverted “C”. The vertical “legs” of the Π shaped seal  415  are the wedges  440  received within valleys  410 . In the illustrated embodiment of  FIGS. 9A and 9B , two concentric loops of wedges  415  are provided. The cover  20  has three concentric loops of ribs  460 ,  465  and  470  spaced apart so that the central rib  465  contacts the first major seal surface  415  substantially between the two concentric loops of wedges  415  and the outer ribs  460  and  470  wipe the lateral portions  445  and  450  of the elastomeric seal  415 . This arrangement keeps elastomeric seal  415  in contact with both the cover  15  and base  20  while mated together. However, when the base  20  is retrieved, the seal  415  “springs” back from contact with the base upper surface  40  thereby avoiding particulate formation that would occur if the seal stuck to base and had to be peeled off by the action of the base manipulator.  
         [0054]     The elastomeric seal  415  may be a solid or hollow member having a shape such as illustrated in  FIGS. 8A and 8B . It may be made of a non-sticky material such as silicone rubber, vinyl chloride resin or other suitable synthetic resin known in the art. In an exemplary embodiment illustrated in  FIG. 11 , the elastomeric seal  415  acts as a spring-damper in conjunction with the reticle support posts  130  and reticle retainer posts  230  to prevent shock and vibration loads on the primary pod  10  from being transmitted to the reticle  30 .  
         [0055]     The above configuration is particularly suitable for utilization of smaller reticles by simply replacing the secondary pod with a pod with inwardly set corner posts  461  as illustrated in  FIG. 10A . The entirety of the primary pod with the isolation features can still be utilized.  
         [0056]     Another embodiment of the container  10  provides for a path to ground for electrostatic dissipation from the patterned surface  50  and the chucking surface  55  of the reticle  30  through the reticle support structure  32  and the reticle retaining structure  34  as well as cover  15  and base  20 . The reticle  30  is thereby protected from ESD. The method and apparatus is discussed in U.S. Pat. No. 6,513,654 to Asyst Technologies Inc., the contents of which are incorporated herein by reference.