Abstract:
A wafer container, and methods of constructing a wafer container. The wafer container has an enclosure portion with at least a top, a bottom, a pair of opposing sides, a back, an open front, and a door to close the open front. The door includes a door chassis with at least a first latching mechanism. The latching mechanism has a rotatable cam member and at least one latching arm. The latching arm has a bifurcate cam follower portion that engages with the periphery of the cam member.

Description:
This application claims the benefit under 35 U.S.C 119(e) of U.S. Provisional Application No. 60/349,068, filed Jan. 15, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally pertains to a wafer carrier designed for supporting, constraining, storing and precisely positioning semi-conductor wafer disks for use in the production of integrated circuits. More specifically, the present invention pertains to latching mechanisms for wafer containers. 
     BACKGROUND OF THE INVENTION 
     Processing of semi-conductor wafers into finished electronic components typically requires many processing steps where the wafers must be handled and processed. The wafers are very valuable, and are extremely delicate and easily damaged by physical and electrical shocks. In addition, successful processing requires the utmost in cleanliness, free of particulates and other contaminants. As a result, specialized containers or carriers have been developed for use during processing, handling and transport of wafers. These containers protect the wafers from physical and electrical hazards, and are sealable to protect the wafers from contaminants. An important characteristic of these containers is that they must be cleanable between uses to ensure that cleanliness is maintained as much as possible. Accordingly, ease of assembly and disassembly of the carrier is a desirable feature. 
     Various configurations of door enclosures and latching mechanisms for sealable wafer carriers are known in the art. Latching mechanisms known in the art often use rotatable cam members. These cam members have typically been formed of planar plastic plates with elongate recesses defining cam surfaces. In early designs, these cam surfaces only provided motion of the cam follower in one direction, typically a single back and forth radial direction that translated to an extension and retraction of the latching portions. Later, a latch motion in the axial direction of the cam member was introduced in order to provide a means of securing the wafer carrier door more tightly for sealing reasons. These axial translation means typically added a substantial number of component parts to the latch assembly. Such additional component parts increase manufacturing costs, increase the complexity of the latching mechanism, increase the difficulty in assembly and disassembly, and increase the number of rubbing and scraping surfaces which generate more particulates. 
     A rotatable cam actuated latching mechanism having an improved cam follower allowing the needed axial movement of a latching arm in addition to simple radial movement was disclosed in U.S. Pat. No. 5,957,292 incorporated fully herein by reference. That invention allowed for a secure door latching mechanism having fewer component parts and with less rubbing and scraping contact, in part due to an s-shaped cam follower that engaged and captured the cam member. The s-shaped cam follower, however, still required cam surfaces defined by an elongated slot in the cam. Such a slotted structure is more difficult to produce than a solid member. In addition, more manipulative steps are required to assemble the cam follower with the cam member. 
     Further improvement to the simplicity and ease of assembly for a door latching mechanism is needed and requires that a cam follower engage and capture the edge of a rotary cam member in some fashion. 
     SUMMARY OF THE INVENTION 
     The present invention fulfills the need for an edge-capturing cam follower for use with a rotary cam member. In the invention, a wafer container having an enclosure portion with at least a top, a bottom, a pair of opposing sides, a back, an open front, and a door to close the open front is provided. The door includes a door chassis with at least a first latching mechanism. The latching mechanism has a rotatable cam member and at least one latching arm. The latching arm has a bifurcate cam follower portion that engages with the periphery of the cam member. The invention provides a simpler latching mechanism while maintaining secure engagement of the cam follower with the cam. 
     An object and advantage of the invention is that the cam follower is securely engaged and captured with the cam member and follows axial as well as radial cam motion. 
     Another object and advantage of the invention is that the cam follower is engaged with the cam member at the edge of the cam member rather than in an elongate slot, simplifying manufacturing of the cam member and assembly of the components. 
     Another object and advantage of the invention is a latching mechanism for a wafer carrier door that is more easily assembled and disassembled for cleaning. 
     Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the wafer carrier and door of the present invention; 
         FIG. 2  is a perspective view of a wafer carrier door; 
         FIG. 3  is a perspective view of the door latching mechanism; 
         FIG. 4  is a cross-sectional view of a currently most preferred embodiment of the cam and cam follower of the present invention; 
         FIG. 5  is a cross-sectional view of an alternative embodiment of the cam and cam follower of the present invention; 
         FIG. 6  is a cross-sectional view of another alternative embodiment of the cam and cam follower of the present invention; 
         FIG. 7  is a cross-sectional view of a currently most preferred embodiment of the cam and cam follower of the present invention showing a step in assembly; 
         FIG. 8  is a cross-sectional view of a currently most preferred embodiment of the cam and cam follower of the present invention showing another step in assembly; and 
         FIG. 9  is a cross-sectional view of a currently most preferred embodiment of the cam and cam follower of the present invention showing another step in assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The accompanying Figures depict embodiments of the wafer container of the present invention, and features and components thereof. Any references to front and back, right and left, top and bottom, upper and lower, and horizontal and vertical are intended for convenience of description, not to limit the present invention or its components to any one positional or spacial orientation. Any dimensions specified in the attached Figures and this specification may vary with a potential design and the intended use of an embodiment of the invention without departing from the scope of the invention. 
     Referring first to  FIG. 1 , a wafer container  100  is seated on automatic processing equipment  10 . Wafer container  100  has an enclosure portion  102 , constructed of polycarbonate plastic, and having a top  104 , a bottom  106 , a pair of opposing sides  108  and  110 , and a back  112 . A door  114  completes the enclosure by enclosing the open front  116  of enclosure portion  102 , fitting into door recess  118 . Wafer supports  120  are provided to support semi-conductor wafers within the enclosure. Kinematic coupling  124 , mounted to the exterior surface of enclosure bottom  106  is provided to facilitate automated handling of the container during use and to provide a reference datum for locating the wafers in the housing during processing. Robotic lifting flange  126  is mounted on the exterior surface of enclosure top  104  and is provided to facilitate automated handling and transport of container  100  during use. 
     Referring to  FIG. 2 , the wafer carrier door  114  of the present invention is depicted. Door  114  is comprised generally of a door chassis  150  and latching mechanisms  160 ,  200 . Mechanism covers  300 ,  302  are provided to protect the latching mechanisms  160 ,  200  from physical damage and contamination and to retain and guide the latching mechanism components. 
     Referring now to  FIGS. 1 ,  2  and  3 , the structure and operation of latching mechanisms  160  and  200  can be understood. In  FIG. 3 , there is shown a partial view of latching mechanism  160 . Latching arms  162  and  164  each have a cam follower portion  166  and  168  respectively, engaged with the periphery  256  of cam member  170  at cam portions  172  and  174 . As depicted in  FIG. 2 , each of latching arms  162  and  164  has a latching portion  176  and  178  at the end opposite from cam follower portions  166  and  168 . When key  220  is inserted into key slot  222  and rotated, cam follower portions  166  and  168  slide along cam portions  172  and  174 . Due to the shape of cam member  170 , latching arms  162  and  164  are translated radially, extending or retracting latching portions  176  and  178  through latch openings  180  and  182 . In addition, cam member  170  may impart motion to latching arms  162  and  164  parallel to the axis of rotation of cam member  170  to draw door  114  more tightly into door recess  118  for sealing purposes. Latching portions  176  and  178  are received by recesses (not shown) in the wafer carrier, allowing the door to be secured in place. 
     A partial cross-sectional view of cam follower portion  166  and cam portion  172  of cam member  170 , in a currently most preferred embodiment of the invention is shown in  FIG. 4 . Cam portion  172 , which is a portion of periphery  256  of cam member  170 , has upper surface  250  and lower surface  252 . Recessed portion  254  is formed in lower surface  252  inward of periphery  256  of cam member  170 . Raised lip  258  is raised from upper surface  250  of cam member  170 . Latching arm  162  has cam follower portion  166 , which is bifurcated into top branch  260  and bottom branch  262 . Top branch  260  extends over cam portion  172  and engages with raised lip  258 , while bottom branch  262  extends under cam portion  172 . Upwardly turned portion  264  of bottom branch  262  engages with recessed portion  254  of cam member  170 . Cam portion  172  is thus held between the furcations of cam follower portion  166 , ensuring that cam follower portion  166  follows cam motion imparted in the axial direction with respect to the axis of rotation of the cam. In addition, cam portion  172  is also held between the furcations of cam follower portion  166  and upwardly turned portion  264 , ensuring cam following in the radial direction. 
     In  FIG. 5 , an alternative embodiment of cam follower portion  166  and cam member  170  is depicted in cross-section. In this embodiment, top surface  250  has raised lip  270  and bottom surface  252  has an opposing raised lip  272 . Cam follower portion  166  is bifurcated into top branch  274  and bottom branch  276 . Cam portion  172  is held between top branch  274  and bottom branch  276 , ensuring that cam follower portion  166  follows cam motion imparted in the axial direction with respect to the axis of rotation of the cam. Top branch  274  and bottom branch  276  each have inwardly turned portions  278  and  280  respectively, which engage raised lips  270  and  272  inward of periphery  256 , holding cam portion  172  and ensuring that cam follower portion  166  follows radial motion imparted by cam member  170 . 
     Another embodiment of the invention is shown in  FIG. 6 . In this embodiment, top surface  250  has raised lip  284 . Again, cam follower portion  166  is bifurcated into top branch  286  and bottom branch  288 . Cam portion  172  is held between top branch  286  and bottom branch  288 , ensuring that cam follower portion  166  follows cam motion imparted in the axial direction with respect to the axis of rotation of the cam. Top branch  286  has an inwardly turned portion  290  that engages raised lip  284  inward of periphery  256 , holding cam portion  172  and ensuring that cam follower portion  166  follows radial motion imparted by cam member  170 . 
       FIGS. 7 ,  8  and  9  illustrate a method of assembly for the embodiment of  FIG. 4 . Top branch  260  is first engaged with lip  258  as shown in  FIG. 7 . As cam follower portion  166  is advanced toward cam member  170 , cam portion  172  fits into the furcation between top branch  260  and bottom branch  262 , as shown in  FIG. 8 . As shown in  FIG. 9 , cam follower portion  166  is rotated downward, and upwardly turned portion  264  engages recessed portion  254 . 
     It will of course be appreciated that, in addition to the specific orientations described above, a variety of other configurations are possible within the scope of the invention. For instance, in the embodiment depicted in  FIG. 4 , the structures could be reversed with raised lip  258  provided on the underside of cam member  170  and recessed portion  254  formed on the top side. In such an embodiment, cam follower portion  166  would also be reversed so that branch  262  is the top branch and branch  260  is the bottom branch. 
     The cam member and cam follower of the present invention can be made from any suitable material or combination of materials. Plastic material is the currently most preferred material for both. Preferably, cam member  170  and cam portion  172  are molded from hard, abrasion resistant material such as PPS, while the latching arms and cam follower are preferably molded from acetal plastic. Carbon fiber or other electrically conductive fill may be added to either to provide conductivity, and PTFE may be added to reduce friction. 
     Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.