Patent Publication Number: US-6662950-B1

Title: Wafer shipping and storage container

Description:
FIELD OF THE INVENTION 
     This invention relates generally to a carrier box assembly for storing and transporting a plurality of thin flat objects including masks, displays, hard disks, silicon wafers and the like, and more particularly for the storage and transport of a plurality of semiconductor wafers. 
     BACKGROUND OF THE INVENTION 
     Various prior art containers have been used in the electronics industry to transport masks, displays, disks, and wafers. The high value and fragile nature of such items requires a very reliable means for supporting them within the container. Many containers are configured specifically for the storage of semiconductor wafers because they are particularly valuable and fragile. 
     Semiconductor wafers are generally circular in shape and very thin. During the wafer manufacturing process, it is often necessary or desirable to move partially completed wafers from a first manufacturing facility to a second manufacturing facility for completion. This requires that the wafers be removed from the first production assembly, then packed and shipped to the second facility, where they are unloaded for further processing, without causing any damage to the wafer. Sources of damage include, but are not limited to, vibration, scraping, or impact during shipping, contamination of the wafer surface, or the destruction of printed circuitry by static electricity. 
     In the past, the handling of wafers by the edges has been preferred in order to prevent damage to, or contamination of, the surface of the wafer. Consequently, known semiconductor wafer carriers have generally stored wafers in stacked cassettes supporting the wafers only at the edges. 
     A continuing trend in the electronics industry is the ever increasing size, and decreasing thickness, of the wafers that must be stored and shipped. As the size and corresponding surface area of the disks increases, and as the thickness of the wafers decreases, new techniques must be found to protect them from damage. The use of rigid supports on the edges of the wafers (prevalent in prior containers) is not sufficiently effective in protecting these larger more delicate wafers. Furthermore, many prior shipping containers have not been well adapted for handling by robotic or automated machinery, thus requiring manual intervention at various stages for loading and unloading. In the processing of semiconductor wafers, there is an inverse relationship between chip yield and particle contamination. Every step requiring manual handling of the wafers increases contamination problems. Concern for particle contamination has increased as chip circuit geometries have decreased, because of the increased potential for contamination by ever smaller particles. 
     What is needed is a wafer carrier that fully supports the wafer in order to avoid damage to the wafer, that protects from the buildup of static charge, that is less expensive to manufacture than previous container designs, and that is configured to allow robotic handling of the carrier, and robotic manipulation of wafer. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is a shipping and storage container for storing and transporting a plurality of disc shaped objects, such as wafers and the like, while preferably protecting the items from vibration, abrasion, impact, particulation, static electricity, and outgassing. Although the embodiments described in this application are configured for holding wafers, the invention could be easily modified by one of ordinary skill for storing other materials including, hard disks, photomasks, liquid crystal displays, flat panel displays, and the like. 
     In its broadest sense, the invention comprises a separable base configured to hold a plurality of wafers stacked one on top of the other within a cylindrical storage area, and a cover configured to fit over portions of the base to enclose the stored wafers. More specifically, the carrier of the invention comprises a base with a deck having at least one wall defining the roughly cylindrical storage area, and a cover including a cylindrical recess or lid configured to fit over and around the vertical wall of the base. 
     In some embodiments, the base of the container includes four roughly identical walls with gaps between the ends of each wall. In other embodiments, these walls are hollow and may be used for holding desiccants, preferably in sealed packages. In various embodiments, the container of the invention also includes a number of useful features, including features used to allow handling of both the container and the wafers by robots or automated machinery, a tamperproof seal, a locking means to prevent accidental opening of the container, stiffening ridges, and data storage means for storing data regarding the contents of the containers. In one embodiment, the locking means is a locking assembly including at least one guide ridge and riser formed on the outer perimeter of one or more vertical walls of the base, and at least one corresponding locking tab formed on the inside surface of the cylindrical recess of the lid. 
     In use, the wafers are placed in vertical stacks within the cylindrical storage area defined by the vertical walls of the base, with lower wafers supporting the underside of upper wafers. Preferably, a protective material, including but not limited to cellulose, a flash-spun and heat-bonded high-density polyethylene (HDPE) fabric that is sold under the tradename a flash-spun and heat-bonded high-density polyethylene (HDPE) fabric that is sold under the tradename TYVEK, or foam discs, are placed between each pair of adjacent wafers. Furthermore, a layer of compressible material is preferably positioned between the top wafer and an underside of the lid. The compressible material fills any void left between the top of the stack and the underside of the lid. It is preferable to overfill the container with the compressive material, so that the overfill creates light compression on the wafers when the container cover is placed over the base, which tends to inhibit wafer movement inside the container, tending to reduce wafer damage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an embodiment of the container of the invention showing the cover of the carrier separated from the base of the carrier. 
     FIG. 2 is a top view of the base of the container of FIG.  1 . 
     FIG. 3 is a bottom view of the base of FIG.  2 . 
     FIG. 4 is a side view of the base of FIG.  2 . 
     FIG. 5 is top view of the cover of the container of FIG.  1 . 
     FIG. 6 is a bottom view of the cover of FIG.  5 . 
     FIG. 7 is a side view of the cover of FIG.  6 . 
     FIG. 8 is a perspective view of an alternate embodiment of the container of the invention with the base comprising only a single vertical wall. 
     FIG. 9 is a side view of the base and cover of the container of FIG. 1, showing a cam and lock mechanism with the cover rotated, relative to the base, into position to begin closing the container. 
     FIG. 10 is a side view of the base and cover of container of FIG. 9 after the cover and base have been rotated into the closed position. 
     FIG. 11 is a side cutaway view of the container of the invention showing a plurality of discs stacked therein. 
     FIG. 12 is a side cutaway view of an alternate embodiment of the container of the invention showing a plurality of discs stacked therein. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a shipping and storage container for storing and transporting a plurality of disc shaped objects, such as wafers and the like, while preferably protecting the items from vibration, abrasion, impact, particulation, static electricity, and outgassing. In its broadest sense, the wafer shipping container of the invention comprises a separable base configured to hold a plurality of wafers stacked one on top of the other within a cylindrical storage area, and a cover configured to fit over portions of the base to enclose the stored wafers. 
     The container of the invention departs from the majority of the prior designs by stacking the wafers in vertical stacks with lower wafers supporting upper wafers. Prior containers typically support the wafers only by the edges of the wafers. A detailed description of several exemplary embodiments of the invention will now be made with reference to the FIGS. 1 through 11, and wherein like features are identified by like numbers. Although the embodiments described herein are configured for holding wafers, the invention could be easily modified by one of ordinary skill for storing other materials including, hard disks, photomasks, liquid crystal displays, flat panel displays, or other items could also be shipped using this system. 
     FIG. 1 shows a perspective view of a first embodiment of the container of the invention, generally referenced by the number  100 . The invention comprises an upper portion or cover  102  and a matching lower portion or base  104 . The base  104  comprises a rectangular deck  110  preferably with a least one wall defining a cylindrical wafer storage area. The wall preferably includes at least one gap, and more preferably, as seen in FIGS. 1 and 2, four vertical walls  106  with a gaps  108  between each pair of walls  106 . Preferred dimensions will be provided for an embodiment of the container  100  of the invention configured to carry an 8 inch wafer, however, the container  100  could be easily modified by one skilled in the art to accommodate other wafer sizes by scaling the dimensions accordingly. 
     Referring to FIG. 3, which shows a bottom view of the base  104 , the deck  110  is preferably square with rounded corners  112 , although any other desired or practical shape may be used. The deck  110  further includes a number of features formed in the bottom surface of the deck  110  including a peripheral flange  120 , a raised cylindrical structure  114 , gripping structures  116 , and raised ridges  118  forming a cross shape with a center square. In alternate embodiments, one or more additional features may be added or one or more of the listed features may be eliminated. 
     The preferred length and width of the deck  110  is approximately 9 {fraction (5/16)} inches square, and the preferred radius of the rounded corners  112  are preferably approximately 1 ⅛ inch, although the actual dimensions of the deck  110  and the radius of the rounded corners  112  may be modified as needed or desired. The peripheral flange  120  is formed around the edges of the deck  110 . In some embodiments, the dimensions of the peripheral flange  120  may be configured specifically for use by robots or automated machinery to manipulate the container  100 . In any case, the dimensions of the peripheral flange  120  are preferably at least adequate to provide rigidity to the edges of the deck  110 . In the embodiment shown in FIG. 3, the height of the peripheral flange  120  from the adjacent bottom surface of the deck  110  is preferably approximately ¼ inch, and the width of the peripheral flange  120  is preferably approximately {fraction (1/16)}. 
     The raised cylindrical structure  114 , which corresponds to a cylindrical depression  122  on the upper surface of the base  104  of the deck  110 , is preferably formed roughly in the center of the deck  110 , and preferably has a diameter of approximately 9 inches. The height of the raised cylindrical structure  114  is preferably slightly less than the height of the peripheral flange  120 , but alternate embodiments could be configured otherwise. 
     Gripping structures  116  are formed near three of the four rounded corners  112  of the deck  110  to provide convenient locations for grasping and handling by machinery or robots. In the preferred embodiment shown in FIG. 3, the gripping structures  116  are preferably circular or “0” shaped with an exterior diameter of approximately ½ inch, and an interior diameter of approximately {fraction (1/16)} inch. However, the particular configuration or shape of the gripping structure  116  may be adapted as necessary to accommodate the machinery or robots that may be used to manipulate the container  100 . Thus, in alternate embodiments, the gripping structures  116  may be virtually any useful shape and size, and may also be positioned in alternative locations. 
     Referring still to FIG. 3, a pattern of raised ridges  118  form a cross pattern on the surface of the raised cylindrical structure  114 , with a center square  124  from which extend three narrow arms  126 , and one wide arm  128 . The ridges  118  preferably perform at least one of the following functions: (1) the ridges  118  may help stiffen the deck  110  of the container  100 , (2) the ridges  118  may be configured to interlink with similar ridges formed on the top of the cover  102  for stability when multiple containers  100  are stacked, and (3) the ridges may be used by robotic or automated machinery to manipulate the container  100 , and (4) the square  124  formed by the ridges  118  may, when interlinked with a similar pattern on the lid of an adjacent stacked container  100 , define a protected area used to store a floppy disk or other data storage media containing information relating to the contents of the container  100 . In the embodiment seen in FIG. 3, the ridges  118  are preferably approximately {fraction (1/16)} inch in width, and approximately {fraction (1/16)} inch in height. The center square  124  is preferably 4 and {fraction (3/16)} inches square. The narrow arms  126  of the cross pattern are defined by two parallel ridges with an approximately ½ inch wide gap between them. The wide arm  128  is defined by two parallel ridges with an approximately ⅞ths inch gap between them. The ridges of the narrow arms  126  preferably end somewhat short of an edge of the raised cylindrical structure  114 , whereas the ridges of the wide arm  128  preferably extend to all the way to the peripheral flange  120 . Referring to FIG. 4, which is a side view of the Base  104  of FIG. 2, the raised ridges  118  extend beyond a plane formed by the peripheral flange  120 . Thus, when sitting on a flat surface, the deck  110  rests upon the raised ridges  118  rather than on the peripheral flange  120 . In alternate embodiments the dimensions and pattern of ridges  118  may be modified as desired, for example, to provide additional or different functional benefit or a different decorative appearance. 
     The corner of the deck  110  that lacks a gripping feature  116  includes, instead, an aperture  130 . As will be discussed in more detail below, when the cover  102  is positioned over the base  104  and rotated into place, the aperture  130  of the deck  110  will align with a matching aperture in the cover  102 . 
     Referring to FIG. 2, the top of the base  104  preferably includes four substantially similar walls  106  formed on the upper surface of the deck  110  of the base  104  at least partially within the cylindrical depression  122 . The walls  106  each have an inner side  132  that, together, define a cylindrical storage region that is preferably approximately 8 inches in diameter. The walls  106  also each have a thickness a height, and an outer side  134 . The outer sides  134  of the walls  106  together define an outer circumference with a diameter of approximately 9 inches. The height of the walls measure approximately 1 ½ inches from the bottom of the cylindrical depression  122  to the top of the walls  106 , and approximately 1 {fraction (5/16)} from the top of the deck  110  to the top of the walls  106 . 
     In the embodiment shown in FIGS. 1,  2 , and  3 , the walls  106  are hollow, forming a chamber  136  within each wall  106 . The wall chambers  136  reduce the amount of material used in the construction of the base, which reduces cost and lightens the container  100 . The chambers  136  can also be used to store desiccants, preferably in pouches, intended to keep the stored wafers dry. The possible or useable size and configuration of the chambers  136  are limited only by the dimensions of the walls  106 . 
     The access gaps  108  are preferably formed between adjacent walls  106 . In some embodiments, the gaps  108  may be required to allow access by a robotic arm or automated machinery to manipulate the wafers (not shown) and any associated packing within the storage area defined by the walls  106 . In use, the preferred robotic arm will gently contact the upper surface of the top wafer with a rubber cup, and use a vacuum formed against the surface of the wafer under the upper cup to lift the disk. The width of the gaps  108  are preferably approximately 1 inch. 
     In alternate embodiments, the number of walls  106  and the configuration and dimensions of the walls  106  may be modified as desired. For example, FIG. 8 shows a perspective view of another embodiment of the a container of the invention with a base  138  having only a single thin wall  140 , with no wall chamber, and only a single access gap  142 . Some alternate embodiments may not require any access gaps at all, and still other embodiments may be configured with more or differently sized and shaped access gaps as required to accommodate selected robotic or automated machinery. 
     Referring to FIGS. 5,  6 , and  7 , the cover  102  preferably comprises a cylindrical recess  152  that defines a cylindrical lid  150  to receive the walls  106  of the base  104 . The cover further preferably comprises a square flange  154 , with rounded corners  158 , formed around the lower edge of the lid  150 . The preferred length and width of the flange  154  is approximately 9 {fraction (5/16)} inches square, and the preferred radius of the rounded corners  112  are preferably approximately 1 ⅛ inch. Any other desired or practical shape for flange  154  may be used, but the shape should preferably be similar to that of the deck  110  of the base  104 . The diameter of the cylindrical recess  152  is somewhat larger than the circumference defined by the outer peripheral surfaces of the walls  106  of the base  104 . The top surface of the cover  102  preferably includes a number of useful features including a pattern of raised ridges  156  forming a cross pattern with a center square and four arms, three narrow arms  168  and one wide arm  170 , preferably corresponding the similar design formed on the bottom of the base  104 . The top surface of the cover  12  preferably also includes a peripheral ridge  160  running around the top of the lid  150 , gripping structures  162  formed on the upper surface of the lid  150  for gripping a data storage medium, and a locking aperture  164  that corresponds to the locking aperture  130  of the deck  110  of the base  104 . However, in alternate embodiments, one or more additional features may be added or one or more of the features may be eliminated. 
     The peripheral ridge  160  is preferably taller than the ridges  156 , and runs around the top of the cylindrical lid  150  as shown in FIG. 5. A pair of alignment notches, best seen in FIG. 7 which is a side view of the cover of FIG. 5, are formed in the peripheral ridge between the ridges of wide arm  170  of the cover  102 . The alignment notches  172  correspond to the ridges of the wide arm  128  of the base  104 . Preferably the stacked containers  100  of the invention will seat properly only when the ridges  118  of the wide arm  128  of the base  104  are aligned with the alignment notches  172  in the top of the container below. The diameter of the peripheral ridge  160  is preferably slightly larger than the diameter of the raised cylindrical structure  114  on the bottom of the base  104  because the circle defined by the peripheral ridge  160  on the lid  150  of the cover  102  is sized to accept the raised cylindrical structure  114  when the containers  100  are stacked. 
     Like the raised pattern of ridges on the bottom surface of the deck  110  of the base  104 , the raised ridges  156  on the top of the cylindrical lid  150  preferably perform at least one of the following functions: (1) the ridges may add additional stiffness of the top of the cover  102 , (2) the ridges may be configured to interlink with similar ridges formed on the bottom of the base  104  of the lower portion when multiple units are stacked, (3) the ridges may be used by robotic or automated machinery to manipulate the container  100 , and (4) the ridges  156  may, when interlinked with a similar pattern on the lid of an adjacent stacked container  100 , define a protected area used to store a floppy disk or other data storage media containing information relating to the contents of the container  100 . 
     The ridges are preferably approximately {fraction (1/16)} inch in width, and approximately {fraction (1/16)} inch in height. The center square  166  measures, preferably, 4 {fraction (5/16)} inches square. The narrow arms  168  of the cross pattern are defined by two parallel ridges with a gap of approximately {fraction (9/16)} inch, the wide arm  168  is defined by two parallel ridges with a gap of approximately 1 a {fraction (1/16)}th inches. Referring to FIG. 7, the raised ridges  156  are less than or equal to the height of a plane defined by the top of the peripheral ridge  160 . In alternate embodiments the dimensions and pattern of ridges  156  may be modified as desired, for example, to provide additional or different functional benefit or a different decorative appearance. 
     Referring again to FIG. 5, the center square  166  formed by the raised ridges  156  on the top of the lid  150  also preferably includes gripping features or locations for holding a selected data storage medium such as a floppy disc, CD ROM, transponder, magnetic strip, bar code, or other storage media. In the preferred embodiment of the cover  102  seen in FIGS. 1 and 5, the gripping structures  162  comprise a pair of pins positioned to snap into the write protect holes on a standard floppy disc. The disc may be used to record the contents of the container, or to transmit other desired data relating to the contents of the containers. 
     As previously mentioned, apertures  130  and  164  are formed in the deck  110  of the base  104  and the flange of the cover  102 , respectively. Together, the apertures  130  and  164 , when aligned, form a hole extending through both the flange  154  of the cover  102  and the deck  110  of the base  104  to accept a portion of a locking apparatus or tamper indicator or tamper proof seal. The preferred tamper indicator comprises a seal that must be destroyed in order to open the container  100 . Acceptable tamper indicators include, but are not limited to, dual sided locking pins showing the logo of the customer, color coded pins, tie wraps, wax seals and metal seals. 
     In a preferred embodiment, the container includes four equally spaced locking elements  187  for preventing or resisting the inadvertent separation of the cover  102  from the base  104  during use. Each locking element  187  comprises a locking tab  182  formed on the inside wall of the cylindrical recess  152 , which interacts with a riser  184  and a guide ridge  186  on the outer surface of the walls  106  of the base  104 . The features can be more clearly seen in FIGS. 9 and 10, which show a side view of a portion of a container with one locking tab interacting with a guide ridge  186  and riser  184 . Referring to FIG. 9, the cover  102  is shown separated from the base  104 , but with the cover  102  rotated relative to the base  104  so that the guide ridge  186  and riser  184  and the locking tab  182  are positioned properly relative to each other to begin the process of closing the container  100 . The cover  102  is lowered over the base  104  until the lower surface of the flanges of the cover  102  rests against the upper surface of the deck  110  of the base  104 . The cover  102  is then rotated relative to the base  104  so that the locking tab  182  is turned into contact with the riser  184 . The locking tab  182  contacts the leading edge of the riser  184  and lifts the cover  102  slightly as the locking tab  182  moves over the riser  184 . The locking tab  182  then slides down the slope of the riser  184  until the locking tab  182  contacts the vertical portion of the guide ridge  186 . The guide ridge  186  guides the locking tab  182  downward towards the deck  110  of the base  104 , and acts to stop the locking tab  182  from rotating further. Once closed, the guide ridge  186  also prevents the locking tab  182  from moving upward relative to the base  104  unless the cover  102  is rotated in the opposite direction. When the cover  102  is rotated in the opposite direction, the riser  186  contacts the locking tab and causes the locking tab  182 , and thus the cover  102 , to lift away from the base  104 . This facilitates removal of the cover  102  from the base  104 , and prevents twisting and scuffing of the wafers  192  caused by the rotation of the cover  102 . All four locking elements  187  are moved into locking position simultaneously as the cover  102  is rotated relative to base  104 . In alternate embodiments, any other known locking means may be used. 
     The material used to form the container  100  is preferably selected to provide a chemically resistant high impact strength container with ESO protection from preferably 10 −3  to 10 −11 . However, in alternate embodiments, any useful or practical material may be used, including any desired plastics and plastic alloys such as a high density polypropolene compound. In some embodiments, various kinds of fibers or other materials may be included in the container  100  to add strength or other desired characteristics. In other alternate embodiments, the materials used in fabrication can be chosen for custom uses, for example, the material used the fabricate the container  100  may be selected for resistance to damage in cold environments or exposure to selected chemicals, such as certain reagents used in the chip fabrication industry, detergents, acids, alkalis, and ultra violet light. The containers  100  may be readily-fabricated in a variety of custom colors, and the colors can be used to color code the containers  100  for easy identification. 
     In some embodiments written information or labeling can be formed directly in the surface of the carrier during fabrication. For example, in the preferred embodiments seen in FIGS. 1 and 5, opening and closing direction indicators are formed on the flange  154  of the cover. 
     FIG. 11 shows a cutaway side view of the container  100 . When the container  100  is loaded, one or more layers of compressible material  196  are placed on the bottom of the cylindrical depression  122  of the base  104 . Then a wafer  192  is placed on the compressible material  196 , followed by another layer or layers of protective material  190 . 
     Referring to FIG. 11, a preferred stacking scheme is shown including a compressible material  196 , such as a urethane foam, placed in the bottom of the cylindrical storage area of the base  104 . Then a layer of protective material  190  is placed on top of the compressible material layer  196 . A wafer  192  is placed on the protective material  190 . The next layers alternate between protective material  190  and wafers  192  until the desired number of wafers  192  are loaded, or until the container  100  is full. An additional layer of compressible material  196  is typically placed on top of the last layer of protective material  190 . The compressive material  190  fills any void left between the top of the stack and the underside of the lid  150 . To prevent breakage of wafers  192  it is important to overfill the container  100  by ¼ to ½ inch. The overfill created light compression on the wafers  192  when the cover  102  is placed over the base  104 . The compression tends to inhibit movement of the wafers  192  inside the container  100  to reduce damage to the wafers  192 . FIG. 12 shows an alternate embodiment of the stacking scheme of FIG. 11, wherein a cylindrical foam insert  194  is positioned around the stack of wafers  192 . In this embodiment, the diameter of the cylindrical storage area defined by the walls  106  must be increased to accommodate the cylindrical foam insert  194 . 
     The preferred urethane foam has a resistivity around 10 11  Ohms/Sq, and meets MIL-B-81705C static decay requirements. The protective material  190  may comprise a flash-spun and heat-bonded high-density polyethylene (HDPE) fabric that is sold under the tradename TYVEK, cellulose, urethane foam, copper intercept, or a combination of such materials. The most preferred protective material  190  is preferably tear resistant, relatively non-particulating, extremely low in sodium content (preferably below 1 PPM), extremely low in sulfur content (preferably below 1 PPM), and resistant to triboelectric charges. If cellulose discs are used, the discs are preferably 100% laboratory-grade low-lint cellulose with low sodium content (preferably around 169 PPM or less), and low sulfur content (preferably around 15-60 PPM or less). The copper intercept may comprise a copper loaded polyethylene or other material. In alternate embodiments, other materials than those described above may be useable, however, acceptable material will preferably be characterized by being non-corrosive, providing excellent cushion properties, providing ESO protection, and having low particulate generation. 
     In the preferred embodiments, loading of the container may be done by hand or with robotic assistance. If a robot is used, the robot is preferably configured to lift the wafer using vacuum suction against the upper surface of the wafer. After the container is loaded and closed, it may be desirable to seal the container in an antistatic film and or metalized bag. The containers may also be placed within cushioned packaging for shipping, such as in a box containing foam padding or any other desired packing material.