Abstract:
A wafer container an enclosure portion including a top wall, a bottom wall, a pair of side walls, a back wall, and a door frame opposite the back wall, the door frame defining a front opening, and a wafer support structure including two side wafer supports 5 each side wafer support including a removable backstop. The invention includes maintaining wafer containers by replacing the removable backstop. The invention includes converting shipping containers that ship large diameter wafers vertically to containers to be used in fabrication facilities that store wafers horizontally for robotic pickup for processing.

Description:
RELATED APPLICATIONS 
     This present application is a National Phase entry of PCT Application No. PCT/US2013/039763, filed May 6, 2013, which claims priority to U.S. Provisional Application No. 61/643,091, filed May 4, 2012, the disclosures of which are incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to containers for sensitive substrates such as semiconductor wafers and in particular to the wafer supporting structures of such containers. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits such as computer chips are manufactured from semiconductor wafers. These wafers are subjected to numerous steps during the process of making integrated circuits. This generally entails transporting a plurality of wafers from one workstation to another for processing by specialized equipment. As part of the processing procedure, wafers may be temporarily stored or shipped in containers to other plants or to end users. Such intra-facility and extra-facility movements may generate or expose the wafers to potential wafer ruining contaminants. In order to reduce the deleterious effect of contaminants on wafers, specialized containers have been developed to minimize the generation of contaminants and to isolate wafers from contaminants exterior to the containers. A principal feature common to these containers is that they are provided with supporting structures to support the wafers inside. 
     Plastic containers have been used for decades for transporting and storing wafers in-between process steps. Such containers have highly controlled tolerances for interfacing with processing equipment as well as the equipment/robots that transport the containers. Moreover, it is desirable in such plastic containers to use components that are attachable and removable without using metallic fasteners such as screws, since metal fasteners can cause particle generation when inserted and removed. 
     Additional, required or desirable characteristics of containers to transport and/or store semiconductor wafers include light weight, rigidity, cleanliness, limited gaseous emissions, and cost effective manufacturability. The containers provide hermetic or close to hermetic isolation of wafers when the containers are closed. Simply stated, such containers need to keep the wafers clean, uncontaminated, and undamaged. Additionally, carriers need to maintain their capabilities under the rigors of robotic handling which includes lifting the carrier by the robotic flange positioned at the top of the container. Further, carriers may be subject to shock from any direction when in transit as well as being subject to changes in orientation when in transit. 
     Front opening wafer containers have become the industry standard for transporting and storing large diameter 300 mm wafers. In such, containers the front door is latchable within a door frame of a container portion, and closes a front access opening through which the wafers are robotically inserted and removed. When the container is fully loaded with wafers the door is inserted into the door frame of the container portion and latched thereto. The enclosure portion generally includes a top wall, a bottom wall, side walls, a back wall, and a door frame defining a front opening. 
     The semiconductor industry is now moving toward using even larger 450 mm diameter wafers. The larger diameter wafers, although providing cost efficiencies, also provide increased fragility, greater weight, and present undiscovered issues associated with handling and storing the larger wafers in containers made of plastic. Deflection and related problems associated with the expanses of plastic on the top, bottom, sides, front, and back are exacerbated. When the carrier door seats and engages the receiving frame of the carrier shell, the door cushion pushes the wafer against a rigid surface or backstop that is located near the rear of the carrier shell. In a carrier, such as a FOUP, used for the transport of wafers in a FAB facility, one of the reasons for alignment with the backstop is to accurately position the wafer radially. This raises several concerns. First, in cases where the wafer retention forces applied by the door cushion are large, contact stresses between the wafer and the backstop can permanently deform the backstop surface. Second, over time, the wafer backstop will wear due to contact with the wafer during carrier transport. The wear can occur due to ordinary transport operation or under conditions of excessive transport vibration. Third, to minimize the above two problems, it may be required for the backstop to be manufactured from a different material than the wafer support. Although a design for a replaceable backstop exists wherein a backstop component is attached to the rear interior wall of the carrier shell, this arrangement tends to cause the wafer position to be inaccurate due to the location of the wafer backstop contact surfaces relative to the center axis of the wafer. 
     A wafer carrier used for shipping wafers, such as a FOSB or MAC generally includes wafer supports that lift the wafers during wafer shipment. If the wafer shipping carrier is then repurposed for use in a FAB, it is no longer desirable for the wafer to be stored in a lifted position. 
     There are several drawbacks associated with prior wafer handling devices or containers related to these issues. In one prior art approach, the wafer backstop is integrated into wafer support. Therefore, the backstop is made from the same material as the wafer support. The wafer support is comprised of a low wear, rigid material. Although the wafer support is designed to endure the contact stresses generated by the retention of the wafer, the backstop will wear over time due to forces normally generated during transport. 
     In another prior art approach, the wafer backstop is overmolded onto the wafer support and is a different material than the wafer support. The overmolded material has high wear resistance and is rigid. Here, although the wafer support backstop is designed to endure the contact stresses generated by the retention of the wafer, the backstop will still wear over time due to forces typically generated during transport. 
     Accordingly, a need in the industry exists for a wafer container that addresses one or more of these problems, particularly as they exist relative to containers for 450 mm diameter and larger wafers. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention address the need of the industry for a wafer container that reduces or alleviates one or more of the problems associated with excessive container wall wear and deformation induces by transport of wafer containers, particularly as those problems are experienced with containers for 450 mm diameter and larger wafers. 
     A wafer container an enclosure portion including a top wall, a bottom wall, a pair of side walls, a back wall, and a door frame opposite the back wall, the door frame defining a front opening, and a wafer support structure including two side wafer supports  5  each side wafer support including a removable backstop. The invention includes maintaining wafer containers by replacing the removable backstop. The invention includes converting shipping containers that ship large diameter wafers vertically to containers to be used in fabrication facilities that store wafers horizontally for robotic pickup for processing. 
     In an embodiment, a front opening wafer container suitable for large diameter wafers uses a wafer backstop that is replaceable and that is formed from a material that has a different modulus than the material that the wafer support shell is formed from. The wafer backstop is formed of a material that has greater wear resistance than the material of the wafer support. The backstop of the present invention is replaceable and includes snap fit style spring members that facilitate removal, replacement and assembly of the backstop within the wafer container shell. 
     In embodiments of the invention the removable backstops engage the wafers at a position about 40 degrees to about 50 degrees each of left and right of rear center. A feature and advantage is that this is an ideal position for centering the wafer for robotic retrieval. 
     According to one embodiment of the invention, a carrier configured for shipping wafers can be configured for transport and storage within a FAB, for example by adding the backstop to each of the side wafer supports. In embodiments, the configuring can also include removal of wafer cushions within the container intended just for shipping; for example, removable cushions at the rear of the container portion, removable cushions at the left front and right front regions forward of the left and right side wafer supports. 
     An advantage and feature of the invention is that a worn backstop can easily be replaced in the field. 
     An advantage and feature of the invention is decreased operational costs because the backstop is replaceable. Instead of replacing an entire wafer support or carrier, only the backstop need be replaced. Currently the replacing of an entire wafer support due to the wear of an integrated backstop requires that the wafer plane associated with the carrier needs to be reaffirmed. 
     Another advantage of the invention is that the radial position of the wafer can be moved to a new position by replacing the wafer backstop according to the present invention. 
     An advantage and feature of embodiments of the invention, especially for a 450 mm case, is that compared to a centrally located replaceable rear backstop, the position of the backstop of the invention located on the wafer support leads to more precise wafer position in the radial direction. Assuming equivalent assembly tolerances, geometric relationships dictate that while rear backstop placement leads to precise wafer position in the y-direction (front to back), it leads to less precise wafer position in x-direction (left to right). The position of the wafer support backstop according to the invention is optimal due to its position balanced between the rear and the side of the carrier. 
     An advantage and feature of embodiments of the invention is that a wafer backstop of a wafer support permanently deforms when wafer retention forces are applied. If the wafer backstop is replaceable then it can also be manufactured using a different material than the wafer support. For example, if the wafer support is comprised of a low modulus material, the replaceable backstop can be formed of a higher modulus material that also has a higher yield strength. 
     A feature and advantage of embodiments of the invention is that the wafer contact surfaces of the backstop are in close proximity to a plurality of positioning stop surfaces and locking members to provide repeatability in wafer positioning when the backstop is replaced. The close proximity minimizes errors such as due to molding deviations or slight misalignments. In an embodiment the wafer contact surfaces are within 1.5 cm of a positioning stop surface. In embodiments within 1 cm. In embodiments, within 2 cm. 
     A feature and advantage of embodiments is that the positioning of the backstop is off of the smaller component, the wafer supports, rather than the prior art alternative, the larger expansive less precise shell portion. The side wafer supports are already required to be precisely positioned to a high degree of accuracy due to the robotic wafer pick up requirements. The back side of the shell, where the prior art wafer stops may be located, do not have the precise positioning requirements and the existence of the vast expanses of polymer in the walls make positioning the stops off of same less precise. 
     Assuming contact stress associated with the applied wafer retention is less than the yield strength of the material, permanent deformation will not occur in the backstop of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the present invention may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
         FIG. 1  is an exploded front isometric view of a front-opening wafer container according to an embodiment of the invention; 
         FIG. 2  is an exploded isometric view of an embodiment of a wafer support assembly for the container of  FIG. 1 ; 
         FIG. 3  is an assembled isometric view of an embodiment of a wafer support assembly of  FIG. 2  for the container of  FIG. 1 ; 
         FIG. 4  is an assembled isometric view of an embodiment of a wafer support assembly of  FIG. 2  for the container of  FIG. 1  according to another embodiment of the invention; 
         FIG. 5  is a front elevational view of a wafer container according to an embodiment of the invention; 
         FIG. 6  is cross sectional view of the wafer container of  FIG. 5  taken on section line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is a front elevational view of a wafer container according to an embodiment of the invention; 
         FIG. 8  is a cross-sectional view taken on section line  8 - 8  of  FIG. 7 ; 
         FIG. 9  is a front elevational view of a wafer container according to an embodiment of the invention; 
         FIG. 10  is a cross-sectional view taken on section line  10 - 10  of  FIG. 9 ; 
         FIG. 11  is a front elevational view of a wafer container according to an embodiment of the invention; 
         FIG. 12  is a cross-sectional view taken on section line  12 - 12  of  FIG. 11 ; 
         FIG. 13  is a front elevational view of a wafer container according to an embodiment of the invention; 
         FIG. 14  is a cross sectional detailed view of a cooperating attachment portion of a side wafer support, specifically a slot for receiving a tab; and 
         FIG. 15  is the cross sectional view of  FIG. 14  with a backstop with a spring catch attached to the side wafer support. 
     
    
    
     While the present invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the present invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention. 
     DETAILED DESCRIPTION 
     For purposes of this application, relative direction may be described in terms of “x” and “y” and “z” directions and these designations relative to the parts of the container are intended to be in accordance with the directional key provided as a part of  FIG. 1 . 
     Referring now to  FIG. 1 , a front opening wafer container  20  generally includes an enclosure portion  22  and a front door  24 . Enclosure portion  22  generally includes top wall  26 , bottom wall  27 , side walls  28 ,  30 , back wall  32 , and door frame  34  defining a front opening  36 . In addition, latch bolt recesses  56  are defined in each of top side  42  and bottom side  46  of door frame  34 . Each latch bolt recess  56  is surrounded by raised portion  58 . Outwardly facing interlock groove  55  is defined at inner edge  57  of door frame  34 . Wafer support structure  60  may be provided inside enclosure portion  22  for receiving wafers in a plurality of slots  62 . A robotic lifting flange  64  and a kinematic coupling  66  as are known in the art may be provided on the top and bottom outer surfaces respectively of enclosure portion  22 . 
     Front door  24  generally includes body portion  68  presenting rear side  70 , front side  72 , top peripheral face  74 , side peripheral faces  76 ,  78 , and bottom peripheral face  80 . A pair of latch recesses (not depicted) are defined in front side  72 , and are covered by front panel  82 . Each latch recess receives a latching mechanism (not depicted), operable by a key insertable though key apertures  84  in front panel  82  to selectively extend and retract latch bolts  86  to engage in latch bolt recesses  56  of container portion  22  to secure front door  24  in door frame  34 . The latch mechanisms can be generally configured as disclosed in U.S. Pat. Nos. 4,995,430; 7,182,203; or 7,168,587, all of which are owned by the owner of the instant application, and all of which are hereby incorporated herein by reference. 
     Referring to  FIGS. 2, 3, 4, 14 and 15 , wafer support structure  60  generally includes two side wafer supports  100  that are generally mirror images of each other. According to the invention, side wafer support  100  has an associated removable backstop  102 . 
     Removable backstop  102  includes wafer engagement portion  104  and an attachment or coupling portion  106 . Wafer engagement portion includes vertically aligned wafer engagement surfaces  108 , longitudinal rearward edge  110 , top edge  112  and bottom terminus  114 . Each of the wafer engagement surfaces  108  is aligned with a respective slot  62  and the top surface  115  of a respective wafer shelf  117 . 
     Coupling portions  106  generally includes alignment members  116  and snap members  118  all configured as horizontally extending tabs. Alignment members  116  may present opening  120  and peripheral ridges  122  extending from body  124 . Snap members  118  may include edge portions  126  and central flex member  128 . Central flex member  128  may present spring or snap catches  130  extending outwardly therefrom that are configured as hook portions  131 . 
     Wafer support structure  60  presents receiving or cooperating attachment portions  132  which are configured as slots  133  to receive coupling portion  106 , configures as tabs, in a complementary fashion. Coupling receiving portion  132  presents alignment member receivers  134  and spring member engagement portion  136  and catch surface  137 . Coupling member  132  has a stop surface  139  that stops the wafer engagement portion of the backstop in approximate radial alignment with the wafer engagement surface  108 . 
     Alignment member receivers  134  and snap member receivers  136 , both defining slots, are separated by intermediate walls  138  backed by back walls  140  and bordered by front walls  142 . 
     Referring to  FIGS. 6, 8, 10 and 12 , side wafer support  100  and removable backstops  102  are depicted in sectional view as situated in enclosure portion  22 . 
     Referring to  FIG. 13  side wafer support  100  and removable backstops  102  are depicted in an unassembled or unattached position and an assembled or attached position. 
     In operation, alignment members  116  and snap or spring members  118  are inserted into alignment member receivers  134  and snap or spring member receivers  136  respectively. Wafer support ramps are then aligned with slots  62  and wafers inserted into slots  62  are then supported to resist movement in both the x and y directions. Thus, wafers are protected against shock that may occur in transit as well as accurately positioned radially. If wafer support portion  104  shows wear after a time, removable backstop  102  can easily be removed by pulling it from side wafer support  100 , by releasing spring or snap members and replaced with a new removable backstop  102  even in the field. PCT/US2011/056944 describes wafer containers with many general features of the present invention and this reference is hereby incorporated by reference herein in its entirety. 
     The foregoing descriptions and the appendices present numerous specific details that provide a thorough understanding of various embodiments of the invention. It will be apparent to one skilled in the art that various embodiments, having been disclosed herein, may be practiced without some or all of these specific details. In other instances, components as are known to those of ordinary skill in the art have not been described in detail herein in order to avoid unnecessarily obscuring the present invention. It is to be understood that even though numerous characteristics and advantages of various embodiments are set forth in the foregoing description, together with details of the structure and function of various embodiments, this disclosure is illustrative only. Other embodiments may be constructed that nevertheless employ the principles and spirit of the present invention. Accordingly, this application is intended to cover any adaptations or variations of the invention. 
     For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section 112, sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim. 
     The above references in all sections of this application are herein incorporated by references in their entirety for all purposes. 
     All of the features disclosed in this specification (including the references incorporated by reference, including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including references incorporated by reference, any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     The invention is not restricted to the details of the foregoing embodiment (s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any incorporated by reference references, any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed The above references in all sections of this application are herein incorporated by references in their entirety for all purposes. 
     Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose could be substituted for the specific examples shown. This application is intended to cover adaptations or variations of the present subject matter. Therefore, it is intended that the invention be defined by the attached claims and their legal equivalents, as well as the following illustrative aspects. The above described aspects embodiments of the invention are merely descriptive of its principles and are not to be considered limiting. Further modifications of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention.