Abstract:
An apparatus for preventing improper engagement of a pod door and a pod. Specifically, misalignment of at least one latch finger connected t the pod door with latch engagement slots in the pod prevents a pod door from mechanically engaging a pod.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/255,467, System For Preventing Improper Insertion of Foup Door Into Foup, by Anthony C. Bonora, Gary M. Gallagher, Michael Ng, filed Dec. 13, 2000, incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to front opening unified pods, or FOUPs, and in particular to FOUPs which include mechanisms for preventing the FOUP door from being improperly inserted into the FOUP. 
     2. Description of Related Art 
     A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment. 
     A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled “SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,” by Mihir Parikh and Ulrich Kaempf,  Solid State Technology , July 1984, pp. 111-115. 
     Systems of the above type are concerned with particle sizes which range from below 0.02 microns (μm) to above 200 μm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half μm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 μm substantially interfere with 1 μm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 μm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles and molecular contaminants become of interest. 
     FOUPs are in general comprised of a vertically oriented FOUP door which mates with a FOUP shell to provide a sealed, ultraclean interior environment in which wafers may be stored and transferred. The wafers are supported either in a cassette which may be inserted into the shell, or to shelves mounted to the interior of the shell. 
     In order to transfer wafers between a FOUP and a process tool within a wafer fab, a pod is typically loaded (either manually or automatedly) onto a load port on a front of the tool so that the pod door lies adjacent the port door of the process tool. Thereafter, latch keys within the port door engage a latch assembly within the FOUP door to decouple the FOUP door from the FOUP, and at the same time couple the FOUP door to the port door. Details relating to such a latch assembly within a pod door are disclosed for example in U.S. Pat. No. 4,995,430, entitled “Sealable Transportable Container Having Improved Latch Mechanism”, to Bonora et al., which patent is owned by the assignee of the present application. The assembly disclosed therein includes a two-stage latching operation to securely latch a pod door to a pod shell as shown in prior art FIGS.  1  and  2 A- 2 B. The latch assembly is mounted within the pod door, and includes a latch hub  28  which engages first and second translating latch plates  30 . The port door includes a pair of latch keys that extend into slots  13  formed in the latch hub to thereby rotate the latch hubs clockwise and counterclockwise. Rotation of each latch hub  28  will cause translation of the first and second latch plates  30  in opposite directions. 
     FIG. 1 is a front view of an interior of the pod door illustrating the latch assembly in the first stage of the door latching operation. When a pod door is returned from its engagement with the port door to the pod, the latch keys within the port door rotate the latch hub  28  to thereby translate the latch plates  30  outwardly so that latch fingers  14  on the distal ends of the latch plates  30  extend in the direction of arrows A into slots  15  formed in the pod shell. The slots  15  conventionally include a transverse wall  17  formed in the pod shell which divides the slot generally in half. The fingers  14  include a space  19  which aligns over the wall  17  when the fingers  14  are received within the slots  15 . 
     FIG. 2A is a side view through line  2 — 2  of the latch assembly shown in FIG. 1, and FIG. 2B is a side view as in FIG. 2A but illustrating the second stage of the door latching operation. In particular, the latch hub  28  further includes a pair of ramps  40  so that, after the fingers  14  have engaged within the slots  15  of the pod shell, further rotation of the hub causes the proximal ends  32  of the latch plates engaged with the hub to ride up the ramps. This causes the latch plates to pivot in the direction of arrows B, about axes lying in the plane of each latch plate and perpendicular to the direction of latch plate translation. The effect of this pivoting during the second stage is to pull the pod door tightly against the pod shell to thereby provide a firm, airtight seal between the pod door and shell. 
     In order to separate a pod door from a pod shell, as when a pod is initially loaded onto a load port interface for wafer transfer, mechanisms within the port door engage the rotatable hub  28  and rotate the hub in the opposite direction than for pod latching. This rotation disengages the latch fingers  14  from the pod shell and allows separation of the pod door from the pod shell. 
     The Semiconductor Equipment and Materials International (“SEMI”) standard relating to FOUP doors requires that the positions of the door mounting features, i.e., the rotatable latch hubs, the fingers on the latch plates and the slots in the FOUP shell, be symmetrical about a horizontal axis. The authors of the standard believed it would be convenient to allow the FOUP door to be inserted into the FOUP right side up or up side down. However, as it turns out, this symmetry of the mounting mechanisms about the horizontal axis provides a significant disadvantage as explained with reference to FIG.  3 . 
     FIG. 3 shows a FOUP  20  housing a plurality of wafers  21 . The FOUP door  22  is conventionally provided with a plurality of protrusions  23  defining a plurality of recesses  24  therebetween. The position of the protrusions  23  and recesses  24  are precision controlled so that upon insertion of the FOUP door  22  into FOUP  20 , the wafers  21  within the FOUP seat within recesses  24  to prevent the wafers  21  from getting dislodged. However, if the FOUP door is inserted up side down, the wafers  21  may not align within recesses  24 , and instead the protrusions  23  may contact the wafers  21 . This is true because in a conventional FOUP, a distance X between a top wafer and the top interior surface of the FOUP is different than a distance Y between the bottom wafer and the bottom interior surface of the FOUP, and thus the position of the protrusions and recesses are not symmetrical about the horizontal axis. Contact between the protrusions on the port door and the wafers can result in damage and/or destruction of each of the wafers within the FOUP. Thus, for 300 mm semiconductor wafers, an improper seating of the FOUP door in the FOUP can result insignificant monetary losses. 
     The error in loading a FOUP door into a FOUP up side down frequently occurs when the FOUP door is manually returned to an empty FOUP. For example, after FOUPs go through a cleaning process, technicians often manually return the FOUP door to the FOUP. FOUP doors are currently marked with an indicator as to which is the top and bottom side of a FOUP door. However, this marking is often overlooked or not understood when a FOUP door is manually inserted into the FOUP. 
     The empty FOUP including the up side down door is subsequently transferred to a load port. As indicated above, conventional load ports operate to transfer the FOUP door to and from the FOUP regardless of whether the door is up side down or right side up. Thus, upon arrival at the load port, the up side down FOUP door is removed as usual and wafers are loaded into the FOUP. However, upon the subsequent return of the FOUP door to the FOUP by the load port, the up side down door is driven into contact with the wafers, and damage and/or destruction of the wafers can occur. 
     SUMMARY OF THE INVENTION 
     It is therefore an advantage of the present invention to provide a system for preventing FOUP doors from improper insertion into a FOUP. 
     It is a further advantage of the present invention to provide a mechanical system which physically blocks a FOUP door from being improperly inserted into a FOUP thereby preventing damage to the wafers therein. 
     It is another advantage of the present invention to provide a mechanical system for preventing improper insertion of a FOUP door into a FOUP without altering or adding to the outer edges or surfaces of a sealed FOUP. 
     These and other advantages are provided by the present invention in which the size, shape and/or location of the latch plate fingers and corresponding slots at the top edge of the FOUP are different than the latch plate fingers and corresponding slots on the bottom edge of the FOUP. Thus, unless the FOUP is correctly oriented right side up upon insertion of the door to the FOUP, the door will not properly fit into the FOUP. Thus, when a sealed FOUP is received at a load port to receive wafers, the FOUP door is right side up and the danger of wafer damage due to an up side down FOUP door is removed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described with reference to the drawings in which: 
     FIG. 1 is a prior art front view of the interior of a FOUP door and shell; 
     FIGS. 2A and 2B are prior art side views of the interior of a FOUP door and shell; 
     FIG. 3 is a prior art side view of the interior of a FOUP showing the recesses within the FOUP door for preventing semiconductor wafers from becoming dislodged when the FOUP is sealed; 
     FIG. 4 is a front view of the interior of a FOUP door and shell according to the present invention including asymmetric top and bottom mounting features; 
     FIG. 5 is a front view of the interior of a FOUP door and shell showing how the mounting features of FIG. 4 prevent coupling of an up side down FOUP door into a FOUP; 
     FIG. 6 is a front view of an interior of a FOUP door and shell showing an alternative embodiment of the asymmetric mounting features for preventing improper insertion of a FOUP door into a FOUP; 
     FIG. 7 is a front view of an interior of a FOUP door and shell showing how the mounting features of FIG. 6 prevent an up side down FOUP door from being coupled to the FOUP; 
     FIG. 8 is a front view of an interior of a FOUP door and shell showing asymmetric mounting features according to a further alternative embodiment of the present invention for preventing improper coupling of a FOUP door into a FOUP; 
     FIG. 9 is a cross section view through line  9 — 9  of FIG. 8; 
     FIG. 10 is a cross section view through line  10 — 10  of FIG. 8; 
     FIG. 11 is a front view of an interior of a FOUP door and shell showing how the mounting features of FIG. 8 prevent an up side down FOUP door from being coupled to the FOUP; 
     FIG. 12 is a cross section view through line  12 — 12  of FIG. 11; 
     FIG. 13 is a cross section view through line  13 — 13  of FIG. 11; 
     FIG. 14 is a front view of an interior of a FOUP door and shell showing asymmetric mounting features according to a further alternative embodiment of the present invention for preventing improper coupling of a FOUP door into a FOUP; 
     FIG. 15 is a cross section view through line  15 — 15  of FIG. 14; 
     FIG. 16 is a cross section view through line  16 — 16  of FIG. 14; 
     FIG. 17 is a front view of an interior of a FOUP door and shell showing how the mounting features of FIG. 14 prevent an up side down FOUP door from being coupled to the FOUP; 
     FIG. 18 is a cross section view through line  18 — 18  of FIG. 17; 
     FIG. 19 is a cross section view through line  19 — 19  of FIG. 17; 
     FIG. 20 is a side view of an interior of a FOUP door and shell showing a further alternative embodiment of the present invention for preventing improper coupling of a FOUP door into a FOUP; 
     FIG. 21 is a side view of an interior of a FOUP door and shell showing the embodiment of FIG. 20 prevents an up side down FOUP door from being coupled to the FOUP; and 
     FIG. 22 is a front view of an interior of a FOUP door and shell showing a further alternative embodiment of the present invention for preventing improper coupling of a FOUP door into a FOUP. 
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described with reference to FIGS. 4-22 which in preferred embodiments relate to a mechanical system for preventing improper insertion of a FOUP door into a FOUP. While the present invention is described with respect to a FOUP for housing 300 mm semiconductor wafers, it is understood that the present invention may be utilized on containers other than FOUPS and other than for housing semiconductor wafers. For example, the present invention may be utilized on bottom opening SMIF pods. Additionally, it is understood that the present invention may be utilized on containers housing workpieces such as reticles and flat panel displays. Moreover, while preferred embodiments of the invention relate to mechanical systems for physically preventing manual insertion of a FOUP door into a FOUP in an incorrect position, in an alternative embodiment, the present invention may operate with sensors to prevent automated insertion of a FOUP door into a FOUP in an incorrect position as explained hereinafter. 
     Referring now to FIG. 4, there is shown a first embodiment of a FOUP according to the present invention including asymmetric top and bottom mounting features. The figure shows a FOUP door  22  fitting within a FOUP shell  25  (only the lower edge of which is shown in FIG.  4 ). With the exception of the latch plate fingers and slots in the FOUP shell described hereinafter, the latch assembly as used to advance and retract the fingers into and out of engagement with the pod shell are not critical to the present invention and they may vary in alternative embodiments. One such latch assembly for use with the present invention is as described in the Background of the Invention section including a two-stage latching operation. Those parts in the figures having like reference numerals to those described in the Background of the Invention section operate as described in the Background of the Invention section. 
     FIG. 4 further shows latch fingers  100  at the distal ends of the top latch plates  30  (reference to top, bottom, upper and lower herein refers to the perspective of the drawing sheets). The fingers  100  are sized and positioned to fit within respective slots  102  in the top edge of the pod shell upon actuation of latch hub  28  and advancing of the top latch plates  30 . The latch assembly further includes fingers  104  at the distal ends  34  of the bottom latch plates  30 . The fingers  104  are sized and configured to fit within respective slots  106  formed in a bottom edge of the FOUP shell. Fingers  104  and slots  106  may be as described in the Background of the Invention section, where slot  106  includes a transverse wall  108  which aligns with a space  110  when the lower latch plates  30  advance fingers  104  into slots  106 . 
     Referring now to FIG. 5, there is shown a FOUP door  22  which is being inserted up side down into the FOUP. As shown, when attempt is made to insert the FOUP door up side down, the fingers  104  are blocked and prevented from entering slots  102  at the top side of the FOUP, and fingers  100  are blocked (by wall  108 ) and prevented from entering slots  106  at the bottom of the FOUP. Thus, if attempt is made to insert the door into the FOUP up side down as shown in FIG. 5, the hub  28  will be prevented from rotating and the FOUP door will not couple to the FOUP. 
     In the embodiments shown in FIGS. 4 and 5, it is understood that the positions of the top fingers  100  and slots  102  on the one hand and the bottom fingers  104  and slots  106  on the other may be switched. It is further understood that other footprints and shapes of the fingers are contemplated than those shown in FIGS. 4 and 5, with the qualification that the top and bottom fingers fit in their respective slots when the FOUP door is properly seated in the FOUP and that at least one of the top pair and bottom pair not fit in the adjacent slot when the FOUP door is improperly seated in the FOUP. 
     Referring now to FIGS. 6 and 7, there is shown an alternative embodiment of the present invention. In this embodiment, the shape of the four fingers  112 ,  116  and slots  114 ,  118  may be identical to each other, but the fingers may be positioned on the latch plates  30  so that the fingers  112  will fit in the slots  114  and the fingers  116  will fit in slots  118  only when the door is positioned right side up. For example, fingers  112  formed on latch plates  30  at the top of the FOUP may be positioned near to the sides of the FOUP, whereas the fingers  116  formed on the latch plates  30  on the bottom of the FOUP may be spaced relatively more inward from the sides of the FOUP. Similarly, the slots  114  in the shell at the top of the FOUP may be located near to the sides, and the slots  118  in the shell at the bottom of the FOUP may be spaced relatively more inward from the sides. In such an embodiment, when the FOUP door is correctly positioned right side up in the FOUP, the fingers at the top and bottom will properly align within the slots at the top and bottom. However, as shown in FIG. 7, when attempt is made to return the FOUP door  22  to the FOUP in an up side down position, the fingers  116  will not align with the slots  114  at the top of the FOUP and the fingers  112  will not align with the slots  118  at the bottom of the FOUP. As would be appreciated by those of skill in the art, the fingers  112 ,  116  maybe placed at other positions on the latch plates than shown in FIGS. 6 and 7, with the provision that the fingers align with the slots when the FOUP door is inserted right side up and that the fingers not align with the slots when the FOUP door is inserted up side down. 
     Up to this point, the invention has been disclosed as varying the positions of the top fingers/slots relative to the bottom fingers/slots in a first dimension (i.e., left to right in the plane of the drawing sheets). However, it is further contemplated that the relative positions of the fingers/slots at the top of the FOUP may be varied relative to the positions of the fingers/slots at the bottom of the FOUP in a second direction (i.e., into and out of the plane of the drawing sheets). One such embodiment is shown in FIGS. 8-13. In this embodiment, the top latch plates may be angled downward from the proximal end to the distal end of the plate (i.e., into the drawing sheet) so that the fingers  120  fit into slots  122  at the bottom of the outer edge  128  in the FOUP shell when the FOUP door is inserted right side up. Similarly, the bottom latch plates may be angled upward from the proximal end to the distal end of the plate (i.e., out of the drawing sheet) so that the fingers  124  fit into slots  126  at the top of the outer edge  130  in the FOUP shell when the FOUP door is inserted right side up. 
     On the other hand, when the FOUP door  22  is inserted up side down, as shown in FIGS. 11-13, the fingers  124  do not align within slots  122  in the upper edge  128  and the fingers  120  do not align within slots  126  in the lower edge  130 . 
     In a further alternative embodiment shown in FIGS.  14 — 19 , the shape of the fingers and slots may be different in the top edge  128  than in the bottom edge  130 . For example, as shown in FIGS. 14-16, fingers  132  fit within slots  134  in the upper edge  128 , and fingers  136  fit within slots  138  at the bottom edge  130 , when the FOUP door  22  is seated in the proper position within the FOUP. However, as shown in FIGS. 17-19, when the FOUP door  22  is improperly positioned in the FOUP, the fingers  136  will not fit within slots  134  at the upper edge  128  of the FOUP, and the fingers  132  will not fit within slots  138  at the bottom edge  130  of the FOUP. It is understood that the shape of the fingers and slots in the upper and lower edges of the FOUP may vary from that shown in FIGS. 14-19 in alternative embodiments, with the provision that the shape of the upper and lower fingers correspond to the shapes of the upper and lower slots when the FOUP door is inserted right side up, and that the shape of the upper and/or lower fingers not fit within the adjacent slots when the FOUP door is inserted into the FOUP up side down. 
     Up to this point, improper insertion of the FOUP door into the FOUP has been prevented by asymmetric mounting mechanisms. However, the FOUP door may be mechanically blocked from mating within the FOUP by other mechanisms in alternative embodiments. One such embodiment is shown in FIGS. 20 and 21. In this embodiment, a pin  140  is fixedly mounted somewhere on the interior of the FOUP shell  25  in a position that does not interfere with the wafers being seated or transferred into and out of the FOUP. Such a position may be for example near the corners or sides of the FOUP. The pin  140  may extend out of the open end of the FOUP such that when the FOUP door  22  is properly seated in the FOUP, the pin  140  is received within a well  142  formed in the interior surface of the FOUP door. However, according to this embodiment, when attempt is made to insert the FOUP door up side down, the well  142  is now located at the opposite end of the FOUP as shown in FIG. 21, so that the pin  140  abuts against the interior surface of the FOUP door  22  to prevent the FOUP door  22  from mating within the FOUP. The pin is preferably formed of a low wear material to minimize particulate generation. 
     The preferred embodiments of the invention described above mechanically prevent a technician from manually coupling a FOUP door to a FOUP in an up side down position. Thus, when a FOUP is received at a load port, it is assured that the FOUP door is in the right side up position, and there is no danger that the FOUP door will contact wafers seated within the load port. It is understood that the various above-described embodiments may be combined with each other to further differentiate the upper fingers and slots from the lower fingers and slots. 
     In a further alternative embodiment, instead of mechanically preventing improper insertion of a FOUP door into a FOUP by a technician, various sensors may be provided at a load port for ensuring that the FOUP door is in the proper orientation before automated return of the FOUP door to the FOUP. For example, as shown in FIG. 22, a hole  150  may be provided through one of the latch plates  30  in the FOUP door. According to this embodiment, a surface in the FOUP door beneath the hole  150  may for example have a greater reflectance than the latch plates themselves. This embodiment may further include an optical sensor such as a retroreflective sensor mounted in the port door to emit a beam out of the port door to the FOUP. The retroreflective sensor is positioned so that, when the FOUP door is properly positioned right side up, the beam from the retroreflective sensor is transmitted through a transparent window (not shown) in the FOUP door cover, which beam passes through the hole  150  and is reflected back to the sensor. However, if the FOUP door is up side down, the beam will not be transmitted back to the sensor, and the controller can then identify that the FOUP door is in an up side down position and should not be returned to the FOUP. In an alternative to this embodiment, the FOUP door cover may itself have a reflective patch on the outer surface of the cover which aligns with an optical sensor in the port door as described above. In such an embodiment, when the FOUP door is properly positioned right side up, the signal from the optical sensor will be reflected back to the sensor from the reflective patch. However, if the FOUP door is up side down, the signal from the optical sensor will not be reflected back. Thus, the controller can determine whether or not the FOUP door is right side up or up side down and return or not return the FOUP door to the FOUP accordingly. 
     Although the invention has been described in detail herein, it should be understood that the invention is not limited to the embodiments herein disclosed. Various changes, substitutions and modifications can be made thereto by those skilled in the art without departing from the spirit or scope of the invention.