Abstract:
A method of and apparatus for reconditioning deformable shipping container fingers used to transport silicon wafers by reforming the fingers to a desired position with or without the use of heat. The apparatus is specifically biased for proper positioning in the shipping container such that the fingers will be fixtured into the desired position. Use of heat in the fixturing process minimizes the amount of time necessary for the fingers to acquire the desired positioning.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates in general to reconditioning of a deformable container for repeated use, and particularly to a method of and apparatus for reconditioning deformable shipping container fingers by reforming the fingers to a desired position with or without the use of heat. Within the wafer industry, it is common to store and ship wafers in an shipping container. Ultrapak® containers and cassettes are manufactured by Empak, Inc. of Colorado Springs, Colo. using polypropylene as a starting material. As Ultrapak® containers are low in cost, no considerable effort has been made for the reuse of the package up until now.  
           [0002]    These containers hold the wafers in cassette that fits within the container and is specially designed to securely hold the wafers. The cassette holds up to wafers. The container itself is comprised of a top and a bottom. When correctly assembled, the three components store and immobilize the cassette loaded with wafers. Fingers molded to the top of the container assembly have a special profile for urging the wafers down into the cassette slots. The fingers provide a key role in avoiding any breakage, rotation, cross-slotting or “rattling” of wafers during their transport. Movement of the wafers in the container can generate particles which can contaminate all of the wafers.  
           [0003]    One of the main obstacles in the reuse of an Ultrapak® container is the loss of the finger tension/elasticity and alignment as a result of any prior wafer storage. Even after a few hours of storage, the fingers loose their elasticity and after opening of the container, they never return to the original, aligned position. Current practice in the industry is to discard the container after a single use, due to the belief it cannot be reused because of the lost elasticity of the fingers. Alternatively, some designs have replaceable fingers. The Ultrapk® does not have replaceable fingers. This would result in lower particle performance of the entire package assembly during wafer transport. Wafer shipping containers must be washed prior to their first use in order to eliminate particles, which affect the quality of the wafers. Wafers are eventually processed into computer chips, and any particle contamination of the wafer results in increased probability that some chips will have to be discarded due to the contamination. It is common to measure the number of particles on a wafer to monitor and measure the efforts to eliminate contamination.  
           [0004]    A single wafer shipping container consists of three pieces: (1) a cassette for holding wafers; (2) a top half of the container; and (3) a bottom half of the container. The cassette has slots for placement of the wafers. The top half of the container has “fingers” which correspond to the slots in the cassette. When assembled, the cassette, container top and container bottom encase and immobilize the wafers and cassette, readying the package for transport. Fingers inside the container top press against the individual wafers, retaining the wafers from undue movement within the cassette slots. Retaining the wafers within the slots helps inhibit breakage, rotation, cross-slotting, or rattling of the wafers during transport.  
           [0005]    Wafer shipping containers of the type described are widely used in the semiconductor industry for packaging and shipping semiconductor wafers. The containers may be formed from polypropylene (a well-known and highly used plastic material of relatively low cost), or any other suitable material. After the first storage of wafers in the container, the fingers deform and bend upwards by engagement with the wafers. After deformation, the containers are no longer useful as the fingers no longer adequately retain the wafers in place for storage and transportation. The particle performance of the entire container is compromised, making the container unusable. As such, the container and cassettes are rarely used more than once, although interest in reuse of these containers has recently grown. A process whereby used wafer shipping containers and other boxes of this type, could be reconditioned for use would be advantageous and beneficial.  
         SUMMARY OF THE INVENTION  
         [0006]    Among the several objects and features of the present invention may be noted the provision of a device and a process for reconditioning wafer shipping containers for reuse; the provision of such a device and process which restore functionality to resilient retaining portions of the container; the provision of such a device and process which reposition the retaining portions in the container after plastic deformation; the provision of such a device which is simple to make and use; the provision of such a device which can hold up under different process conditions such as heat treatment and washing of the container; the provision of such a device which is capable of being easily placed and removed within the container; the provision of such a device sized such that it will place the retaining portions of the container in the proper position when fitted properly into the container top; and the provision of such a process which can be carried out simultaneously with other container reconditioning processes.  
           [0007]    A method of the present invention is for reconditioning deformed retaining portions of a container used for positioning articles in the container by application of a resilient holding force on the articles. The fingers have a deformation history through prior use of the retaining portions to hold articles in the container such that at least some of the retaining portions are no longer capable of applying the same resilient holding force to the articles. This method generally comprises the steps of: (1) fixturing the retaining portions by placement of a fixture to hold the retaining portions in a position selected to substantially restore the function of the retaining portions to be able to apply a resilient holding force to articles in the container, and (2) substantially erasing the deformation history of the retaining portions by holding the retaining portions in said selected position until the retaining portions are reconditioned for use to be able to apply said resilient holding force to articles in the container.  
           [0008]    In another aspect of the present invention, a device for fixturing the aforementioned resilient fingers of a container generally comprises means for placing the fingers in a position to recondition retaining portions deformed from the use of holding articles to a recycled condition capable of applying a selected holding force for holding articles in the container. Also, the devise comprises means for holding the placing means in self-retained position against the fingers.  
           [0009]    In still another aspect of the present invention, a device for fixturing the aforementioned resilient retaining portions of a container. The device comprises a first positioning member sized and shaped for placement between the retaining portions and a portion of the container for separating a first group of the retaining portions and one container portion to position the first group of retaining portions in a proper position to recondition the retaining portions. It also has a second positioning member sized and shaped for placement between the retaining portions and another portion of the container for separating a second group of the retaining portions and another container portion to position the second group of retaining portions in a proper position to recondition the retaining portions. There is a connector connecting the first and second positioning members.  
           [0010]    Other objects and features will be in part apparent and in part pointed out hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective of a container used to ship semiconductor wafers with a top of the container exploded and partially cut away to show the fingers in the container lid which retain the wafers when wafers are stored in the container;  
         [0012]    [0012]FIG. 2 is a transverse section of the container in a closed and sealed configuration and holding a wafer;  
         [0013]    [0013]FIG. 3 is an enlarged fragment of FIG. 2 illustrating a desired undeflected position of the fingers in phantom along with a wafer stored in a slot;  
         [0014]    [0014]FIG. 4 is an enlarged fragment similar to FIG. 3, but with the wafer removed and illustrating a device for fixturing the fingers of the present invention;  
         [0015]    [0015]FIG. 5 is an enlarged fragment similar to FIG. 4 but illustrating a device of a second embodiment;  
         [0016]    [0016]FIG. 6 is a plan view of the device of the first embodiment of the invention, with parts broken away to show a spring within the H-shaped device;  
         [0017]    [0017]FIG. 7 is a top plan view of the second embodiment of the invention.  
         [0018]    Corresponding reference characters indicate corresponding parts throughout several views of the drawings;  
         [0019]    [0019]FIG. 8 graphs the force applied by the resilient retaining portions of a container over time, showing the results for an unused container, a used and retensioned container, and a container used twice without retensioning container;  
         [0020]    [0020]FIG. 9 shows the deflection of the resilient retaining portions of a container as a function of force for a reused and retensioned container, a container used once only, and a contained reused twice; and  
         [0021]    [0021]FIG. 10 illustrates the point on a finger where the tensioning portions of the container were measured to prepare FIGS. 8 and 9. 
     
    
       [0022]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring now to the drawings, FIG. 1 shows a container (generally indicated at  100 ) used to store and transport any kind of a thin, flat object, but particularly a wafer used to produce semiconductor chips. Container  100  includes a top  105  having a curved upper surface  130  and a fitted edge  120  that forms a tight seal with the bottom of the container  300 . Fingers  110  and  111  (broadly, “retaining portions”) are opposed and aligned so that the upper portions of individual wafers will fit between opposing pairs of fingers. In the illustrated embodiment, the fingers  110 ,  111  are formed as one piece with the container top  105 . The distal ends of the fingers  110  are bifurcated into tip portions  112  and the distal ends of the fingers  111  are bifurcated into tip portions  113 . Only one of the tip portions  112 ,  113  of the fingers  110 ,  111  can be seen in FIG. 2, the other of the tip portions being located on the opposite side of the wafer  400 . A gap (not shown) between the tip portions  112 ,  113  of each finger receives a short peripheral request of the wafer  400 . A cassette  200  fits within the bottom of the container  300 . The cassette has rows of opposing grooves  210  and  211  in which individual wafers may be placed. The cassette  200  is open at the bottom. The bottom of the container  300  is curved in general conformance with the shape of the peripheries of the wafers stored in the container  100 . The bottom of the container  300  has a lip  320  that runs around the edge of the bottom of the container, and seals with the fitted edge  120  of the top of the container  100 . The illustrated container is the ULTRAPAK® shipping container commercially available from the Empak, Inc. of Colorado Springs, Colo.  
         [0024]    A wafer  400  fits snugly within the container. The wafer  400  is tightly held within a single row formed by an aligned pair of the grooves  210 ,  211  designated at  212  and  213 , respectively. Transversely opposed pairs of fingers  110 ,  111  engage each wafer  400  with one tip portion  112 ,  113  disposed on one side of the wafer and the other tip portion disposed on the other side of the wafer. Engagement with the wafer  400  deflects the fingers  110 ,  111  upwardly from their initial relaxed positions, illustrated in phantoms in FIG. 3. The fingers  110 ,  111  resist the deflection and bear against the wafer  400 , holding it down in the grooves  212 ,  213  and resisting movement of the wafer relative to the container  100  and the other wafers in the container. Curved top  130  of the container and curved bottom  340  of the container provide adequate room in the container to fit the profile of the circular wafer  400 . After storing a wafer for only a brief time, the fingers  110  and  111  become plastically deformed. In this case, the fingers are not positioned correctly (the phantom lines in FIG. 3 indicate proper positioning) to retain the semiconductor wafer in place for safe shipment and/or storage.  
         [0025]    According to the present invention, a reconditioning device  500  can be positioned to recondition all of the deformed fingers  110 ,  111 . In a first preferred embodiment, the device  500  has a generally “H” shape (see FIG. 6), including a pair of legs  510 ,  520  joined together by a cross piece generally indicated at  522  (FIG. 4). A first element  530  of the cross piece  522  is fixedly joined to leg  522  and telescopingly received in a tubular second element  540  fixedly joined to leg  520 . A coil compression spring  540  disposed in the second element  540  has end caps  542  receiving the ends of the spring. One of the end caps engages the leg  520  and the other end cap engages the free end of the first element  530 , biasing the first element  530  outward of the second element  540  and, accordingly, urging the legs  510 ,  520  apart from each other. Referring to FIG. 4, the device  500  can be compressed, moving the legs  510 ,  520  closer together so that the device can be moved upwardly between the opposing rows of fingers  110 ,  111  and released so that the legs move outwardly between the upper surface  130  of the top  105  of the container  100 . The legs  510 ,  520  are disposed between the curved upper surface  130  and the fingers  110 ,  111 , pushing the fingers downward. The spring  530  allows the device  500  to hold itself in a self-retained position (shown in FIG. 4) in the top  105 . The force of the spring  540  and the diameter of the legs  510 ,  520  are selected so that the fingers  110 ,  111  are relocated to a position at or slightly below their original, undeformed positions. A more detailed discussion of the method of the present invention employing the device  500  will be described hereinafter.  
         [0026]    A second embodiment of the device (designated generally at  600 ) is shown in FIG. 7 to comprise legs  610 ,  620  similar to the legs  510 ,  520  of the device  500  of the first embodiment. However, the legs  610 ,  620  are joined together by a torsion spring  630  having a first end connected to the leg  610  and a second end connected to the leg  620 . In a relaxed condition of the spring  630 , the legs  610 ,  620  are located relatively closer together so that they may be passed upwardly between the opposed rows of fingers  110 ,  111 . Counter rotation of the legs  610 ,  620  about the axis of the spring  630  moves the legs further apart so that they fit between the fingers  110 ,  111  and the curved upper surface  130  of the top  105  forcing the fingers down to the position at or slightly below their original, undeformed position. The torsion induced in the spring  630  by the counter rotation of the legs  610 ,  620  causes the legs to be biased outwardly against the surface  130  of the top  105  of the container  100 . Thus, the device  600  is capable of retaining itself in position on the top  105 .  
         [0027]    Having described the device ( 500 ,  600 ) of the present invention, a preferred method of use will be described. Reforming the fingers  110 ,  111  to substantially their initial positions after use is ideally done during the normal wash cycle of the container  100 . The container is washed in any event before the initial and every subsequent use of the container to reduce the potential for contaminating the wafers. After the first and every subsequent use, the fingers  110 ,  111  will be permanently deformed from their initial positions, thus defining fingers having a “deformation history”. In this deformed position, some or all of the fingers  110 ,  111  are not capable of applying the same resilient holding force that they did when in their original undeformed positions. The method of the present invention substantially erases the deformation history so that the fingers  110 ,  111  can apply nearly the same resilient holding force to subsequent wafers.  
         [0028]    The fingers  110 ,  111  are first fixtured in a position which is at or slightly beyond their original undeflected position by inserting the legs ( 510 ,  520  or  610 ,  620 ) of the device ( 500  or  600 ) between the fingers and the curved upper surface  130  of the top  105 . Although either device ( 500  or  600 ) could be used, the remainder of the description will assume device  500  is being used for simplicity. The top  105  with the device  500  is then subjected to a normal wash in which the temperature is about 50° to 60° C. The heat of the wash substantially removes the stress of the fingers  110 ,  111  as deflected by the device  500  back to their original positions. The container top  105  is brought back down to room temperature with the device  500  remaining in place to locate the fingers. Thereafter, the device is removed and the container  100  is ready for reuse. Instead of raising the temperature of the box, the device  500  could be left in the top  105  for longer periods of time (in a clean room environment) to achieve the desired repositioning of the fingers  110 ,  111 . Of course, the reconditioning process will take substantially longer (e.g., several days) in the latter instance.  
         [0029]    Containers  100  of the preferred embodiment (i.e., an ULTRAPAK® shipping container) are made primarily of polypropylene having a glass transition temperature of about −10° C. While not bound by the following theory, it is generally believed that using the device above the glass transition temperature of the plastic leads to satisfactory results. For example, the reformation of the fingers  110 ,  111  using the device  500  which is carried out at a temperature of 45°-60° for a period of about 10 minutes produces satisfactory results. The times and temperatures experienced by the container top  105  in the standard Atcor wash cycle designed for particulate removal are sufficient to produce the desired repositioning of the fingers  110 ,  111 . The following examples illustrate the efficacy of the device  500  and method of the present invention.  
       EXAMPLE  1   
     Visual Verification of the Realignment in Different Times and Conditions  
       [0030]    Two Ultrapak® shipping containers  100  were tested. Nine wafers were loaded in slots  1 - 3 ,  11 - 13  and  23 - 25  of the two containers. Both containers were stored for approximately one week. After unloading the wafers, the amount of deflection was measured at the end of the used fingers. The average deflection was approximately 100 thousandth of an inch per container (2.5 mm) as measured at location  810  in FIG. 10. Next, the containers were washed in a standard Atcor washer, one container having the device  500  of FIG. 6 and one without the device. After removing the device from the “fixtured” top  105 , the alignment of the fingers was checked visually. Although the deflection of the fingers of the non-“fixtured” box has also decreased, only in the case of the fingers that were “fixtured” using the device  500  during the wash cycle, was complete realignment achieved. No notable change in the position of the realigned fingers was observed even several weeks after the insert removal.  
       EXAMPLE  2   
     Comparative Measurements of the Finger Tension  
       [0031]    Alignment and elasticity of the fingers through the “fixturing” process was measured. Two 200 mm Ultrapak® shipping containers  100  were loaded with nine wafers each (slots  1 - 3 ,  12 - 14  and  23 - 25 ) and stored at room temperature for 6 days. After this storage interval and after unloading the wafers, the fingers corresponding to the wafer occupied slots were visibly out of alignment from the standard position. The deflections ranged between 30-50 thousandths of an inch (0.76-1.27 mm) as measured at location  800  in FIG. 10. Next, both boxes were subjected to a normal Atcor cleaning cycle, with one of the boxes having the fingers “fixtured” with the device of FIG. 6.  
         [0032]    After removing the insert, all the fingers were aligned and apparently were capable of retaining that position for times as long as 72 hours. Then, dummy wafers were loaded in both containers and they were staged at room temperature for 6 days. The results on the elasticity decay for the 3 sets of fingers, “Used Once”, “Reused and retensioned” and “Reused Only” are shown in FIGS. 8 and 9. In one test, one finger from each group was deflected by 90-93 thousandths of an inch (2.28-2.36 mm) as measured at location  800  in FIG. 10 by pressing with the probe of an Imada DPS11R force gauge. The decay of the reactive stress of the finger was measured. The differences between the decays for all the finger groups were not significant. Next, the fingers were pressed down, reaching a constant deflection value, and the reactive tension of the finger was monitored at different time intervals. In FIG. 9 the average results of  11  fingers tested from each of the “Used Once”, “Reused and retensioned” and “Reused Only” groups is given. The remaining reactive tension in each of the fingers was recorded at 2 minutes after the stress was applied at different deflection values. All the measurements were made by applying the stress with the tip of the Imada probe at the point indicated in the FIG. 10.  
         [0033]    The test results indicate that there is no statistical difference between the three sets of measurements.  
       EXAMPLE  3   
     Particle Performance of the Reused Boxes with Realigned and Retensioned Fingers  
       [0034]    This test monitored the particle performance for three 200 mm Ultrapak® containers:  
         [0035]    CASE A: Control  
         [0036]    A standard Ultrapak® shipping container was washed using the normal Atcor conditions and then placed into use.  
         [0037]    CASE B: Reused Ultrapak® 
         [0038]    A standard Ultrapak® shipping container was loaded with 9 dummy wafers and stored for one week in a cleanroom. After unloading the wafers, the package was washed using the normal Atcor conditions. It was then reloaded with wafers and reused a second time. The fingers were deflected from the first use.  
         [0039]    CASE C: Reused and Retensioned Ultrapak® 
         [0040]    A standard Ultrapak®) shipping container was loaded with 9 dummy wafers and stored for 1 week in the cleanroom. After unloading the wafers, the container was washed in Atcor with the fingers “fixtured” in the realigned position using the device of FIG. 6.  
         [0041]    Next, 75 wafers were scanned on a KLA-Tencor SP-1 auto-inspection tool using a 0.12 mm threshold particle recipe. The wafers were loaded into the three boxes, which after bagging, were transported to a cleanroom, where they were unpackaged and stored for approximately 3 days.  
         [0042]    The boxes were re-bagged and sent to their original packaging site, where they were re-inspected in the same conditions. After this storage and handling interval, which took 1 week, the wafers were re-scanned in the same conditions. In all three cases (A-C) the top of the boxes had the fingers equally deflected.  
         [0043]    The particle performance of handling and storing the wafers in each case A-C was evaluated by 2 methods (see Table 1): 1) the total particle counts were counted and compared before and after the handling and storage; 2) using Excel macros, particles on the same wafers, before and after handling and storage were matched by location, and the new “Added Particle” counts were calculated and used in the comparison. This later comparison method allowed comparison of the newly “Added” and “Moved” particles, eliminating the impact of “Totally Removed” particles from the wafer surface during the process. By both evaluation methods, the best particle performance was found on Case C—Reused and Retensioned.  
         [0044]    The repeated ability to reuse and rewash containers helps to continuously remove particles from the inside of the container, thus making it more difficult for contamination.  
                                                                                                           TABLE 1                           Particles found on test wafers before and after storage and handling       in new and reused Ultrapak® boxes                Case   Case C (Reused                Case A (Control)   B (Reused)   and Retensioned)            Counts   Total   Per/wafer   Total   Per/wafer   Total   Per/wafer                    Initial   688   27.52   849   33.96   252   10.08       Particles       Final   688   27.52   853   34.12   247   9.88       Particles       Initial-Final    0   0    4   0.16    −5     −0.2       Standard   —   10.00   —   11.25   —   9.24       Deviation       Matching   687   27.48   847   33.88   242   9.68       Particles       Added    44   1.76    43   1.72    5   0.2       Particles                  
 
         [0045]    In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.  
         [0046]    When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.  
         [0047]    As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.