Abstract:
A front opening wafer carrier formed principally of plastic and comprising an enclosure portion and door has a path to ground with respect to the wafers, the path to ground effectuated by the door. The base “ground” may be provided at the machine interface upon which the carrier sits, or through the robotic arm that grasps, operates and moves the door.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 10/496,756, filed Apr. 11, 2005, (U.S. Pat. No. 7,886,910 issuing Feb. 15, 2011), which application is a 371 of PCT/US02/37926, filed Nov. 26, 2002, which claims benefit of U.S. Provisional Application No. 60/333,682, filed Nov. 27, 2001. Said applications are herein incorporated by reference herein in their entirety. 
     
    
       [0002]    The processing of wafer disks into integrated circuit chips often involves several steps where the disks are repeatedly processed, stored and transported. Due to the delicate nature of the disks and their extreme value, it is vital that they are properly protected throughout this procedure. One purpose of a wafer carrier is to provide this protection. During processing of semiconductor wafers or magnetic disks, the presence or generation of particulates presents very significant contamination problems. Contamination is accepted as the single largest cause of yield loss in the semiconductor industry. As the size of integrated circuitry has continued to be reduced, the size of particles which can contaminate an integrated circuit has also become smaller, making minimization of contaminants all the more critical. 
         [0003]    Wafer Carriers configured as enclosures for holding wafers intermediate processing steps are typically formed of numerous plastic components assembled together. The industry accepted configuration for larger wafers, that is 300 mm wafers, is to have an enclosure portion with a lower machine interface configured as a kinematic coupling, an open front closeable by a door, and stacked wafer shelves on the inside sides of the enclosure portion. A door with a pair of latching mechanisms sealingly closes the open front and will typically have wafer restraints that contact and restrain the forward edge of the wafers in the enclosure. 
         [0004]    Conventional carriers used in the semiconductor industry may develop and retain static charges. Static buildup on carriers can cause semiconductor processing equipment to automatically shut down. It is desirable to have a carrier with static dissipation characteristics to control static charges. 
         [0005]    A undesirable effect of static charges is exhibited when a charged plastic part comes into contact with an electronic device or processing equipment of a significant different potential it may discharge in a damaging phenomena known as electrostatic discharge (ESD). These discharges can be catastrophic during the processing of wafers into semiconductors. Means are known to provide grounding of wafers for minimizing the occurrence of such discharges. See for example U.S. Pat. No. 5,711,082 to Nyseth, owned by the owner of the instant invention. 
         [0006]    Contaminants in the form of particles may be generated by abrasion such as the rubbing or scraping of the carrier with the wafers or disks, with the carrier covers or enclosures, with storage racks, with other carriers, or with the processing equipment. It is critical to keep contaminants off of the wafers. The polycarbonate plastic shell of wafer carrier enclosures are known to naturally have a slightly negative charge. Grounding of the wafer shelves and thus the wafers within the enclosure can render the wafers with no electric charge causing particles to be attracted to the plastic enclosure rather than the wafers. See U.S. Pat. No. 5,944,194 to Gregerson, Gallagher, and Wiseman, owned by the owner of the instant invention. The U.S. Pat. Nos. 5,711,082 and 5,944,194 patents are incorporated herein by reference. These references provide background information, as well as the configuration and construction of wafer carriers, and illustrate means of conventionally providing paths to ground. 
       SUMMARY OF THE INVENTION 
       [0007]    A front opening wafer carrier formed principally of plastic and comprising an enclosure portion and a door has a path-to-ground with respect to the wafers effectuated by the door. The base “ground” may be provided at the machine interface upon which the carrier sits, or through the robotic arm that grasps, operates and moves the door. Several alternate paths for the path to ground include the following: 
         [0008]    1) From the robotic arm operating the door, for example, key receiving portions of said arm, through conductive components in the door such as the latching mechanism, to a conductive wafer restraint that is mounted on the door for engaging the wafers. 
         [0009]    2) From the machine interface upon which the carrier sits, to a conductive door contactor portion that contacts a portion of the door when the door is moved into position on the carrier, to the conductive wafer restraints on the door. 
         [0010]    3) From the machine interface upon which the carrier sits, to a moveable conductive active wafer restraint attached within the enclosure portion, to the wafers. 
         [0011]    4) From the robotic arm operating the door, for example, the key insert portions of said arm, through conductive components in the door such as the latching mechanism, to a conductive contactor portion extending from the door to an active wafer restraint mounted within the enclosure portion. The active wafer restraint may be actuated by a fixed conductive contactor portion or by an active contactor portion operated by the latching mechanism of the door. 
         [0012]    The conductive components may be formed, for example, from carbon fiber or powder filled polymers, metallic composites, conductive film coated ceramics, or conductive film insert molded polymer components. 
         [0013]    An object and advantage of preferred embodiments of the invention is that a path to ground for the wafers is established through the door. 
         [0014]    An object and advantage of preferred embodiments of the invention is that a path to ground for the door may be established before the wafers come into contact with the wafer restraints thereby minimizing the chance of a potential between the door and wafer causing a static discharge. 
         [0015]    An object and advantage of preferred embodiments of the invention is that potential between the door and wafers is eliminated before the cushions mounted on the door come into contact with the wafers. 
         [0016]    An object and advantage of preferred embodiments of the invention is that alternative or additional paths to ground are provided. The conventional path to ground circuit is from the wafers through the column of wafer support shelves to the lower machine interface which is grounded through contact with grounded equipment or support base. The alternative circuits are as described above. These may be in lieu of or supplemental to the conventional path and further provide the elimination of potential with the wafer contacting components of the door. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0017]      FIG. 1  is a perspective view of a front opening wafer container carrier in accordance with the invention herein. 
           [0018]      FIG. 2  is a perspective view of a door of a wafer carrier in accordance with the invention herein. 
           [0019]      FIG. 3  is a perspective view of a door housing with latch mechanism compartments exposed illustrating insert molded components providing a path to ground. 
           [0020]      FIG. 4  is an exploded view of an enclosure portion of a wafer carrier with latch mechanism exposed in accordance with the invention herein. 
           [0021]      FIG. 5  is a perspective view of a components of a latching mechanism and key suitable for the doors illustrated herein. 
           [0022]      FIG. 6  is a perspective view of an enclosure portion and door of a wafer carrier with portions cut away illustrating an embodiment of the invention herein. 
           [0023]      FIG. 7  is a plan cross-sectional view of a portion of a wafer carrier illustrating a further embodiment of the invention. 
           [0024]      FIG. 8  is a perspective view with sections cut-away of an enclosure portion of the wafer carrier of  FIG. 7  in accordance with the invention herein. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    Referring to  FIGS. 1 , and  2 , a wafer carrier according to the invention is illustrated and is principally comprised of an enclosure portion  20  for holding wafers  22  and a door  24 . The enclosure portion has a top  28  with a robotic lifting flange  29 , a bottom  30  with a machine interface piece  32 , a pair of sides  34 ,  36 , side handles  40 , a door frame  44 , an open front  46 , and a open interior  48 . The door has an outside surface  56 , and inside surface  58 , wafer restraints  60 , latch compartments  64 ,  66 , and key slots  68 ,  70 . Robotic arms  69  with keys for engaging the door are illustrated with dashed lines. The wafer restraints when mounted on the door may be passive, that is, fixed on the door, or active, as illustrated in U.S. Pat. No. 5,711,427, which is incorporated herein by reference. 
         [0026]    As illustrated in  FIGS. 3 ,  4 , and  5 , a path-to-ground from the wafers may be effectuated through the door latching mechanism  71  and wafer restraints. When used herein, “conductive and static dissipative polymers” mean polymers with surface resistivity of less than about square and preferably less than 10 8  ohms per square. The specific surface resistivity appropriate may vary depending on the component and path to ground circuit. Conductive plastic pieces  74 ,  76  may be insert molded into the door housing  77  to provide a conductive path from the mechanism to the mounting receptacles  84  for the wafer restraints. The wafer restraints are formed of conductive material, preferably a carbon filled polymer such as PEEK. The insert molding of the conductive plastic pieces  74 ,  76  may be accomplished by insert molding of rigid pieces such as illustrated in U.S. patent application Ser. No. 09/317,989, filed May 25, 1999, and owned by the owner of this invention. Said application is hereby incorporated by reference. Also insert molded plastic conductive film may be utilized on components of the door to create the path to ground  80  illustrated by the dashed lines. See U.S. Provisional Patent Application 60/333,686, filed Nov. 27, 2001, and entitled Polymer Film Insert Molding for Providing Electrostatic Dissipation, owned by the owner of this invention and incorporated herein by reference. The door latching mechanism  71  has a cammed hub  91  and a pair of link arms  93 ,  95  that have latching portions  98 ,  99  that extend out apertures  100  in the door housing. The caromed hub will typically be molded of plastic with carbon filler to provide static dissipative characteristics and has a pair of cam surfaces  104  that are engaged by a cam followers  107  on the cammed hub. The cammed hub  91  also has a key hole  110  for receiving the key  112  which would, pursuant to this embodiment of the invention, be grounded and part of a robotic operating arm. Thus, in this embodiment, the grounded key  112  is inserted into the key hole  110  and makes contact with the conductive cammed hub. The cammed hub rotates on and contacts protrusion  113  as part of the conductive piece of the door housing. The conductive wafer retainers either may directly contact the conductive piece of the door housing or a conductive mounting receptacle  84 . When the door is placed on the enclosure portion by the robotic arm, the latching mechanism is grounded by the key and when the wafer restraints contact the wafers they a path-to-ground is provided. In an alternative embodiment the door housing may be made of conductive plastic eliminating the conductive piece. 
         [0027]    Referring to  FIG. 6 , an alternative means of providing a path-to-ground effectuated by the door is illustrated. In this embodiment, the machine interface piece  32 , is formed of conductive plastic and has three slots, not shown in this embodiment, forming a kinematic coupling in said piece. A conductive door contacting piece  190 , configured as an arm, extends from the interface piece and is appropriately positioned to contact the door when the door is closed onto the enclosure portion. In a preferred embodiment, the arm may directly contact the wafer restraint, which will also be formed of conductive plastic. In a related embodiment a conductive plastic arm may extend from the door, be conductively connected to wafer restraints, and contact the grounded machine interface piece as the door is closing. The arm in these embodiments may be angled and have a thinned elongate portion to facilitate bending during and after engagement with the respective components. Other embodiments may have curved compressible spring sections. Thus, in this embodiment, the path-to-ground conductive circuit is effectuated from the machine interface which is grounded on the equipment or fixture upon which the container is placed. The path-to-ground circuit extends from the machine interface to the door through a container-door bridging component configured as an arm, and then to the wafer restraints. Preferably the container-door bridging component makes the connection between the door and the enclosure portion before the wafer restraints contact the wafers. 
         [0028]    Referring to  FIGS. 7 and 8 , an alternative embodiment of the invention is illustrated. In this embodiment the enclosure portion has a movable wafer restraint mechanism pivotally attached to the enclosure portion and configured as a pivotal elongate wafer contacting member  194 . The wafer contacting member or wafer restraint pivots to bring a wafer engaging portion  96  into restraining and conductive contact with the wafers as illustrated in  FIG. 8 . The pivoting action of the wafer restraint is effected by an actuation member  198  extending from the door and the conductive elongate wafer contacting member rotates about a conductive pin  201  engaged in apertures  202  on appropriate grounded support portions on the bottom of the wafer enclosure portion. A similar pin receiving aperture may be on the top of the wafer enclosure. Depending on the configuration of the wafer restraint, the actuation member can be passive, to actuate the wafer restraint by simply closing the door, or can be active to operate by actuation of the latching mechanism  199 . When the door is moved into the closure position, the door actuation member  198  engages with the actuation member to move same into an contact and restraining position with the stack of wafers. In this embodiment, the further door wafer restraints  204  may or may not be utilized. If utilized, the door wafer restraints may be grounded by way of actuation member engaging the grounded elongate wafer contacting member. 
         [0029]    Thus the invention functions as follows: when the enclosure portion has a wafer stack or wafer positioned therein, the door is moved into place, either manually or by robotic means. In the preferred embodiment, the wafer restraints are grounded by completion of a path to ground before the wafer restraints come into contact with the wafers. 
         [0030]    The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is, therefore, desired that the present embodiment be considered in all respects as illustrative and not restrictive