Patent Publication Number: US-2003234208-A1

Title: Container with magnifying identification lens

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to containers used in the storage and transport of semiconductor wafers in a semiconductor fabrication facility. More particularly, the present invention relates to a wafer container fitted with a magnifying lens or lenses to facilitate quick and accurate identification of wafers in the container.  
       BACKGROUND OF THE INVENTION  
       [0002] A standardized mechanical interface (SMIF) system is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. Such a SMIF system is designed to reduce particle fluxes onto semiconductor wafers and/or reticles in a semiconductor production facility. The SMIF system prevents or minimizes particle contamination of the wafers during transport and storage of the wafers by ensuring that gaseous media surrounding the wafers is essentially stationary relative to the wafers, and further, by preventing exposure of the wafers to particles from the ambient environment.  
       [0003] The SMIF concept is based on the use of a small volume of motion- and contamination-controlled, particle-free gas to provide a clean environment for semiconductor wafers and other articles. Further details of one such system are described in a 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.  
       [0004] SMIF systems are designed to prevent contamination by particles which range from below 0.02 μm to above 200 μm. Due to the small geometries of the components in modern semiconductor integrated circuits, particles falling within this size range can significantly adversely affect semiconductor processing. Current geometry sizes for semiconductor integrated circuits have reached less than half a micron, and those circuits are adversely affected by particles having a size as small as 0.01 μm. In the future, semiconductor integrated circuits will be marked by increasingly smaller geometry sizes, requiring protection from contamination by correspondingly smaller particles.  
       [0005] In a typical SMIF system, semiconductor wafers are stored and transported in wafer cassette containers, or pods, and are transferred from the pod to processing or testing equipment typically in the following manner. First, the pod is placed at the interface port of a processing tool. Each pod includes a box and a box door designed to mate with doors on the interface ports of the processing equipment enclosures. Then, latches release the box door, and the box door and the interface port door are opened simultaneously such that particles which may have adhered to the external door surfaces are trapped or sandwiches between the box and interface port doors. A mechanical elevator lowers or translates the two doors, with the cassette riding on top, into the enclosure-covered space. The cassette is transferred by gravity or a manipulator and placed onto the cassette platform of the equipment. After processing, the reverse operation takes place.  
       [0006]FIG. 1 illustrates a typical conventional SMIF pod  10  used in conjunction with a port assembly  12  on a canopy of a semiconductor processing tool or station (not illustrated). The SMIF pod  10  includes a pod cover  14  having multiple cover sides  16 , a flanged cover base  20  and a cover top  22 . When removably attached to the cover base  20  of the pod cover  14 , a pod door  18  of the SMIF pod  10  supports a wafer cassette  24  (FIG. 2) holding multiple semiconductor wafers  1  inside the pod cover  14 . The SMIF pod  10  is used to transport the wafers  1  such as from one processing or testing tool or station to another in the semiconductor production facility, typically by the use of overhead transport vehicles (OHTs) or automatic guided vehicles (AGVs).  
       [0007] After it arrives at the appropriate processing tool or station in the facility, the SMIF pod  10  is initially placed on a port door  28  of the port assembly  12 . An elevator assembly (not illustrated) then lowers the port door  28 , which lowers the pod door  18  and the wafer cassette  24  supported on the pod door  18  from the interior of the pod cover  14 , through a port plate  26  of the port assembly  12  and into a minienvironment (not illustrated) beneath the canopy of the processing tool. After processing of the wafers  1 , the port door  28  is actuated by the elevator to lift the pod door  18  and wafer cassette  24  upwardly through the port plate  26 , at which time the pod door  18  is re-attached to the cover base  20  of the pod cover  14  with the wafer cassette  24  and wafers  1  sealed in the reassembled SMIF pod  10 .  
       [0008] During processing of semiconductor wafers at the various processing tools or stations, groups or “lots” of wafers are manufactured together in batches. Each wafer within a lot is processed at the same time and under the same conditions as all the other wafers in the lot. Each wafer lot is assigned a serial number, or “lot number”, and within each lot, each wafer is assigned a unique serial number.  
       [0009] For a number of reasons including quality control, wafer manufacturers find it useful to track wafer lots as they travel from one station or tool to another in the facility. A reliable method of identifying the wafers by lot number is therefore very important for accurate tracking of the wafers. To properly identify the wafers by lot throughout the fabrication process, identification marks must be placed on each wafer. Because all of the wafers in a SMIF pod are in the same lot, the pod cover is typically constructed of a clear or transparent material to facilitate visual lot identification of the wafers therein by facility personnel without requiring removal of the pod cover from the pod door.  
       [0010]FIG. 2 illustrates a wafer  1  supported by a wafer cassette  24  inside a SMIF pod  10 . The wafer  1  is visible through the clear or transparent cover top  22  of the pod cover  14 . Typically, a lot number  8  is inscribed by a laser adjacent to the wafer edge  4  in the silicon layer on the patterned side of the wafer  1  where electronic devices are built. Facility personnel can thus visually read the lot number  8  through the transparent cover top  22  of the pod cover  14  and thus, monitor or track the course of the SMIF pod  10  through the facility and make any necessary adjustments in transport of the SMIF pod  10 . Alternatively, the lot number  8  may be provided on the wafer cassette  24  or on the inside surface of one of the cover sides  16  or on any other suitable element inside the SMIF pod  10 .  
       [0011] Because the lot number  8  inscribed on the wafer  1  or provided elsewhere inside the SMIF pod  10  is typically small, however, it is often difficult for facility personnel to accurately visually read and identify the lot number  8  through the pod cover  14  without first removing the SMIF pod  10  from a transporting vehicle or stocker. In some cases, a magnifying glass (not illustrated) may be held adjacent to the pod cover  14  after removal of the SMIF pod  10  from the transport vehicle or stocker to render the lot number  8  easier to read. This procedure is time-consuming and interrupts orderly and timely transport of the wafers  1  throughout the facility.  
       [0012] Accordingly, a device is needed for facilitating quicker and more accurate visual determination of the lot number on a semiconductor wafer or elsewhere in a wafer container.  
       SUMMARY OF THE INVENTION  
       [0013] An object of the present invention is to provide a device for the accurate identification of items in a container.  
       [0014] Another object of the present invention is to provide a device and method for the timely and accurate identification of an identification number inside a container for an item or items in the container.  
       [0015] Another object of the present invention is to provide a device for the accurate identification of semiconductor wafers in a wafer pod or container.  
       [0016] Still another object of the present invention is to provide a mechanism for the accurate identification of semiconductor wafers in a standard mechanical interface (SMIF) pod without the need for interrupting orderly and timely transport of the SMIF pod from one location to another in a semiconductor fabrication facility.  
       [0017] Yet another object of the present invention is to provide a mechanism which contributes to orderly and accurate transport of semiconductor wafers in a semiconductor fabrication facility.  
       [0018] Still another object of the present invention is to provide a mechanism for quick and accurate identification of semiconductor wafers in a wafer container or pod without first requiring removal of the wafer container or pod from a transport vehicle or stocker in a semiconductor fabrication facility.  
       [0019] A still further object of the present invention is to provide a mechanism which facilitates quick and accurate identification of the lot number of semiconductor wafers in a wafer pod or container.  
       [0020] Yet another object of the present invention is to provide a method of facilitating quick and accurate identification of semiconductor wafers by lot number or other category as the wafers travel from one processing tool or station to another or as the wafers are stored in a stocker in a semiconductor fabrication facility.  
       [0021] In accordance with these and other objects and advantages, the present invention comprises a wafer pod or container fitted with at least one magnifying lens for magnifying the image of a lot number or other identifying indicia typically inscribed on a wafer inside the pod or container. The magnifying lens enables quick and accurate visual identification of the wafers by lot number or other identifying indicia as the wafers are transported in a semiconductor wafer fabrication facility.  
       [0022] The lot number or other wafer-identifying indicia may be inscribed on a wafer or wafers inside the container or pod or provided on a wafer cassette or other element inside the wafer container or pod. Accordingly, the magnifying lens or lenses may be provided in the top or one or more sides, or both, of the wafer container or pod to facilitate magnification of the identifying indicia inside the container or pod and accurate and timely tracking and/or correction in the course of travel or storage of the wafers throughout the semiconductor production process, as necessary. The magnifying lens or lenses may have any desired magnification power, typically but not necessarily in the range of from about 2× to about 50× magnification power.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023] The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
     [0024]FIG. 1 is an exploded, perspective view of a typical conventional SMIF pod, used in conjunction with a port assembly of a standard mechanical interface on a wafer processing tool or station;  
     [0025]FIG. 2 is a top view of the wafer cassette container or pod illustrated in FIG. 1, with a wafer substrate contained inside the container or pod and a lot number inscribed on the wafer visible through the transparent pod cover thereof;  
     [0026]FIG. 3 is a perspective view of an illustrative embodiment of a wafer container or pod of the present invention;  
     [0027]FIG. 4 is a cross-sectional view, taken along section line  4 - 4  in FIG. 3; and  
     [0028]FIG. 5 is a top view of the wafer container or pod of the present invention, in typical application of the invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0029] When used herein, the term cover shall be understood to mean any object capable of partially or completely enclosing one or more articles. When used herein, the term identifying indicia shall be understood to mean any marking, writing or inscription consisting of numbers, letters or both, provided on a surface to identify an article or articles. When used herein, the term magnifying lens shall be understood to mean any plastic or glass lens capable of magnifying an image of an object.  
     [0030] The present invention has particularly beneficial utility in the quick, accurate and convenient identification of semiconductor wafers inside a wafer container or pod used to transport or store the wafers in a semiconductor production facility. However, the invention is not so limited in application, and while references may be made to such wafer container or pods, the invention may be applicable to the quick and accurate identification of items in a closed container in a variety of industrial and product applications.  
     [0031] In an illustrative embodiment, the present invention is directed to a wafer pod or container having at least one magnifying lens provided in the top or side thereof, or both, for magnifying the image of a lot number or other identifying indicia either inscribed on a wafer inside the pod or container or provided on a wafer cassette or other element in the container. The magnifying lens or lenses enable facility personnel to quickly and accurately identify the wafers by lot number or other identifying indicia inside the pod or container as the wafers are transported or stored in a semiconductor wafer fabrication facility.  
     [0032] Referring to FIGS.  3 - 5 , an illustrative embodiment of the wafer container of the present invention is generally indicated by reference numeral  35  and may be a SMIF pod or any other type of wafer transport or storage container known by those skilled in the art. The wafer container  35  typically includes a pod cover  37  having multiple cover sides  40  and a cover top  39 . The pod cover  37  may be constructed of clear polycarbonate, Lexan or any other clear or transparent material. Alternatively, the pod cover  37  may be constructed of an opaque or colored plastic or other material. A cover base  47  may be provided at the bottom end of the pod cover  37  for removably receiving a pod door  38 . A latch mechanism (not illustrated), which may be conventional, is used to removably latch the pod door  38  on the cover base  47  and seal a wafer cassette  43  (FIG. 5) holding multiple semiconductor wafers  45  inside the pod cover  37 .  
     [0033] A magnifying lens  41 , which may be oval, as illustrated, or any other suitable shape, is typically seated in a lens opening  42  which extends through the cover top  39 , as illustrated in FIG. 4. It is understood that various other configurations may be used to seat or attach each magnifying lens  41  to the pod cover  37 . The magnifying lens  41  may be formed of Lexan or any other transparent magnifying glass or plastic. A magnifying lens  41  is typically located adjacent to one or more cover edges  44  where the cover top  39  meets the respective cover sides  40  of the pod cover  37 . In the embodiment illustrated in FIG. 3, a pair of magnifying lenses  41  is provided in the cover top  39 , adjacent to opposite cover edges  44 . However, it is understood that either one magnifying lens  41  or multiple magnifying lenses  41  may be provided in the cover top  39  at any location or locations therein to facilitate visual image magnification and identification of identifying indicia  49  inside the wafer container  35 , as illustrated in FIG. 5 and hereinafter further described. A magnifying lens or lenses  41  may alternatively or additionally be provided in one or more of the cover sides  40 , as illustrated in phantom in FIG. 3. The magnifying lens or lenses  41  may be provided anywhere on the pod cover  37  in sufficient viewing proximity to identifying indicia  49  for the wafers  45  inside the wafer container  35 . Each of the magnifying lenses  41  may have any desired magnification power or strength, but the magnification power of the magnifying lenses  41  is typically in the range of from about 2× to about 50×.  
     [0034] Application of the wafer container  35  of the present invention is as follows. Identifying indicia  49 , typically including a lot identification number, is inscribed by a laser (not illustrated) adjacent to the wafer edge  46  of each of the multiple semiconductor wafers  45  in a common lot at the beginning of the semiconductor production process. Multiple wafers  45  in the same lot are loaded onto a wafer cassette  43 , which is supported on the pod door  38  of the wafer container  35 . The pod door  38  is then removably attached to the cover base  47  preparatory to transporting the wafers  45  in the wafer container  35  throughout the semiconductor fabrication facility. Instead of being inscribed or otherwise imprinted upon the wafers  45 , the identifying indicia  49  may be provided on the wafer cassette  43 , on the inside surface of one of the cover sides  40 , or on any other suitable supporting element inside the wafer container  35 . In the case of the wafer container  35  illustrated in the drawings, the identifying indicia  49  inscribed on the top wafer  45  on the wafer cassette  43  is positioned beneath one of the magnifying lenses  41  provided in the cover top  39  upon placement of the wafer cassette  43  and wafers  45  in the wafer container  35 . Accordingly, the image of the identifying indicia  49  is magnified and rendered easily visible through the magnifying lens  49  in such a manner that the identifying indicia  49  can be readily, accurately and conveniently identified by facility personnel tracking the lot of wafers  45  throughout the facility. This identification procedure can be performed without first requiring the removal of the wafer container  35  from the transport vehicle or stocker (not illustrated) and then replacement of the wafer container  35  back on the transport vehicle or stocker after identification, which would significantly reducing lag time in the transport of the wafer container  35  and wafers  45  throughout the facility.  
     [0035] While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.