Abstract:
A cover or housing which spans an output port of a first station and an input port of a second station in a manufacturing facility, for example, and covers or houses a conveyor extending between the stations for conveying articles from the first station to the second station. A source of nitrogen gas or clean dry air is provided in communication with the housing interior, and at least one exhaust fan is provided on the housing. As articles are conveyed from the first station to the second station, nitrogen gas or clean dry air is blown into the housing and drawn therefrom through the exhaust fan or fans, such that the flowing gas or air removes particles from the articles as they are carried to the second station.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to a stocker conveyor in an automatic material handling system and more particularly, relates to a conveyor which is equipped with a nitrogen or air purge for blowing potential contaminating particles from pods, containers or articles transported using the conveyor.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the manufacturing of a product, the product is usually processed at many work stations or processing machines. The transporting or conveying of partially-finished products, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The careful conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chip must be transported between various process stations in order to facilitate various fabrication processes.  
           [0003]    For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching, and passivation must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e., a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.  
           [0004]    Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically-guided vehicles (AGVs) or overhead transport vehicles (OHTs) that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes or SMIF (standardized mechanical interface) pods and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle. The AGVs and OHTs normally transport the pods from bay to bay along an interbay loop, and eventually deliver the pods to a robotic storage house, or “stocker”, which automatically delivers the pods to an intrabay loop.  
           [0005]    In an automatic material handling system (AMHS), stockers are widely used in conjunction with automatically guided or overhead transport vehicles, either on the ground or suspended on tracks, for the storing and transporting of semiconductor wafers in SMIF pods or in wafer cassettes. For instance, as shown in FIG. 1 of the drawings, three possible configurations for utilizing a stocker are illustrated. In case A, a stocker  10  is utilized for storing WIP wafers in SMIF pods and transporting them first to tool A, then to tool B, and finally to tool C for three separate processing steps to be conducted on the wafers. After the processing in tool C is completed, the SMIF pod is returned to a stocker  10  for possible conveying to another stocker. The configuration shown in case A is theoretically workable but hardly ever possible in a fabrication environment, since the tools or processing equipment cannot always be arranged nearby to accommodate the processing of wafers in the stocker  10 .  
           [0006]    In the second configuration, case B shown in FIG. 1, a stocker  12  and a plurality of buffer stations A, B and C are used to accommodate three different processes to be conducted in tool A, tool B and tool C, respectively. As shown in FIG. 1, a SMIF pod may be first delivered to buffer station A from the stocker  12  and waits there for processing in tool A. Buffer stations B and C are similarly utilized in connection with tools B and C. The buffer stations A, B and C therefore become holding stations for conducting processes on the wafers. This configuration provides a workable solution to the fabrication process, but requires excessive floor space because of the additional buffer stations required. The configuration is therefore not feasible for use in a semiconductor fabrication facility.  
           [0007]    In the third configuration, shown as case C in FIG. 1, a stocker  14  is provided for controlling the storage and conveying of WIP wafers to tools A, B and C. It is seen that after a SMIF pod is delivered to one of the three tools, the SMIF pod is always returned to to the stocker  14  before it is sent to the next processing tool. This is a viable process since only one stocker is required for handling three different processing tools and no buffer station is needed. The configuration shown in case C illustrates that the frequency of use of the stocker is extremely high since the stocker itself is used as a buffer station for all three tools. The accessing of the stocker  14  is therefore much more frequent than that required in the previous two configurations.  
           [0008]    [0008]FIG. 2 illustrates a schematic of a typical automatic material handling system  20  that utilizes a central corridor  22 , a plurality of bays  24  and a multiplicity of process machines  26 . A multiplicity of stockers  30  are utilized for providing input/output to the bay  24 , or to processing machines  26  located on the bay  24 . The central corridor  22  designed for bay layout is frequently used in an efficient automatic material handling system to perform lot transportation between bays. In this configuration, the stockers  30  of the automatic material handling system become the pathway for both input and output of the bay. Unfortunately, the stocker  30  frequently becomes a bottleneck for internal transportation. It has been observed that a major cause for the bottlenecking at the stockers  30  is the input/output ports of the stockers.  
           [0009]    In modern semiconductor fabrication facilities, especially for the 200 mm or 300 mm FAB plants, automatic guided vehicles (AGV) and overhead transport vehicles (OHT) are extensively used to automate the wafer transport process as much as possible. The AGV and OHT utilize the input/output ports of a stocker to load or unload wafer lots, i.e., normally stored in SMIF pods. However, in the current configuration and design of stockers, an AGV or OHT when approaching a stocker blocks both the input and the output ports even though it only performs a single operation of either loading or unloading. This is shown in FIGS. 3 and 4.  
           [0010]    [0010]FIG. 3 is a perspective view of an overhead transport vehicle system  32  consisting of two vehicles  34 ,  36  that travel on a track  38 . While both an input port  40  and an output port  42  are provided on the stocker  30 , the overhead transport vehicle  36  stopped at the position for unloading a lot  44  into the input port  40 , effectively blocks the access to the output port  42 . As a result, the other overhead transport vehicle  34  waits on the track  38  for input from stocker  30  and cannot access the stocker until the overhead transport vehicle  36  has moved out of the way. The arrangment shown in FIG. 3 results in considerable time loss since the stocker  30  can only be accessed for either input or output, but not both simultaneously. This significantly affects the efficiency of the input and output operations of the stocker  30 .  
           [0011]    A conventional automatic guided vehicle (AGV) system used in a conventional stocker configuration is shown in FIG. 4. The AGV system  48  consists of two automatic guided vehicles  50  and  52  with vehicle  52  stopped in front of the stocker  30 . The stocker  30  is equipped with an input port  54  and an output port  56 . As shown in FIG. 4, the automatic guided vehicle  52  approaches the output port  56  for accepting an output from stocker  30 , but at the same time, the input port  54  is also blocked by the vehicle  52  such that the second vehicle  50  must wait for input until the vehicle  52  has moved out of the way. The conventional stocker  30  therefore cannot be efficiently operated since the input port  54  and the output port  56  cannot be accessed by automatic guided vehicles simultaneously to perform loading and unloading at the same time.  
           [0012]    Another conveyor system frequently used in manufacturing facilities includes a conveyor belt system in which an endless belt traverses multiple rollers to carry articles from one location to another. These conveyor belt systems include stocker conveyors which provide a useful mechanism for transport of semiconductor wafer pods into stockers in semiconductor production facilities. However, the pods often accumulate potential wafer-contaminating particles during such transport. Accordingly, the pods carry the particles to the stockers and eventually, to the processing stations, where the particles increase the likelihood of wafer contamination upon subsequent internalization of the pods into the load ports of the processing stations.  
         SUMMARY OF THE INVENTION  
         [0013]    Accordingly, an object of the present invention is to provide a system for removing particles from articles carried on a conveyor.  
           [0014]    Another object of the present invention is to provide a system for removing particles from semiconductor wafer pods carried on a conveyor in a semiconductor production facility.  
           [0015]    Still another object of the present invention is to provide a stocker conveyor particle removing system which utilizes a continuous flow of nitrogen gas or clean, dry air (CDA) flow to remove particles from the surfaces of a semiconductor wafer pod as the pod is transported into a wafer stocker in a semiconductor production facility.  
           [0016]    Yet another object of the present invention is to provide a stocker conveyor particle removing system which includes an ionizer or static electricity remover for removing particles from a wafer pod before nitrogen- or air-induced removal of the remaining particles from the wafer pod.  
           [0017]    A still further object of the present invention is to provide a stocker conveyor particle removing system provided with a stopping and starting mechanism for automatically initiating and terminating, respectively, operation of the system as needed.  
           [0018]    In accordance with these and other objects and advantages, the present invention comprises a cover or housing which spans the output port of a first station and an input port of a second station in a manufacturing facility, for example, and covers or houses a conveyor extending between the stations for conveying articles from the first station to the second station. A source of nitrogen gas or clean dry air is provided in communication with the housing interior, and at least one exhaust fan is provided on the housing. As articles are conveyed from the first station to the second station, nitrogen gas or clean dry air is blown into the hosuing and drawn therefrom through the exhaust fan or fans, such that the flowing gas or air removes particles from the articles as they are carried to the second station. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0020]    [0020]FIG. 1 is a schematic view illustrating three possible configurations for utilizing a stocker in a manufacturing facility;  
         [0021]    [0021]FIG. 2 is a schematic view of a typical automatic material handling system which utilizes a central corridor, a plurality of bays and a multiplicity of process machines;  
         [0022]    [0022]FIG. 3 is a perspective view of a conventional overhead transport vehicle (OHT) system;  
         [0023]    [0023]FIG. 4 is a perspective view of a conventional automatic guided vehicle (AGV) system;  
         [0024]    [0024]FIG. 5 is a side view of a conventional stocker conveyor in a semiconductor production facility;  
         [0025]    [0025]FIG. 6 is a side view of an illustrative embodiment of the stocker conveyor particle removing system of the present invention;  
         [0026]    [0026]FIG. 7 is a sectional view, taken along section lines  7 - 7  in FIG. 6, of the housing component of the stocker conveyor particle removing system of the present invention;  
         [0027]    [0027]FIG. 8 is a top view, partially in section, of the stocker conveyor particle removing system of the present invention;  
         [0028]    [0028]FIG. 9 is a side view of another illustrative embodiment of the stocker conveyor particle removing system of the present invention; and  
         [0029]    [0029]FIG. 10 is an enlarged sectional view of the housing component of still another illustrative embodiment of the stocker conveyor particle removing system of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    When used herein, the term, “gas” shall mean nitrogen gas, clean dry air or other inert gas. When used herein, the term, “article conveyor” shall mean any conveyor belt, automatically it guided vehicles (AGVs) or overhead transport vehicles (OHTs) used to transport articles in a manufacturing or other facility. Therefore, while references may be made to stocker conveyors which utilize a conveyor belt to transport articles from one location to another, the present invention contemplates other types of transport apparatus as suitable for implemetation of the present invention.  
         [0031]    The present invention has particularly beneficial utility in application to removing potential wafer-contaminating particles from wafer pods in semiconductor production facilities. However, the invention is not so limited in application and while references may be made to such semiconductor production facilities, the invention may be more generally applicable to removing particles from articles in a variety of industrial and product applications.  
         [0032]    Referring initially to FIG. 5 of the drawings, a typical conventional stocker conveyor used in semiconductor production facilities is generally indicated by reference numeral  1 . The stocker conveyor  1  operates in a clean room environment and includes an endless conveyor belt  2  that is used to continually transport wafer pods  8  from the output port of a station  4 , which may be a wafer processing station, a wafer pod storage station or other station, and into the input port of a stocker  6 . From the stocker  6 , the pods  8  are transported by means of automatic guided vehicles (AGVs), overhead transport vehicles (OHTs) or additional conveyor belts  2  to processing stations or other destinations in the semiconductor production facility.  
         [0033]    Although the stocker conveyor  1  operates in a clean room environment, such an environment is not completely free of dirt, dust and other particles which have the potential to contaminate integrated circuits on the wafers contained in the pods  8  during the subsequent wafer processing steps. Accordingly, the transport interval between the station  4  and the stocker  6  provides additional occasion for dirt, dust and other potentially contaminating particles to collect on the surfaces of the pod  8 , particularly the bottom surface thereof.  
         [0034]    An illustrative embodiment of the stocker conveyor particle removing system of the present invention is generally indicated by reference numeral  60  in FIGS.  6 - 8  of the drawings. The stocker conveyor particle removing system  60  includes an elongated cover or housing  61  which is connected to the output port of the station  4  at an entry end  65  and to the input port of the stocker  6  at an exit end  66  and defines a housing interior  62  (FIG. 7) that spans the station  4  and stocker  6 . The housing  61  is typically constructed of plexiglass® or any other anti-ESD material. The conveyor belt  2  of the conventional stocker conveyor  1  extends through the housing interior  62 , as illustrated in cross-section in FIG. 7. Multiple conduit openings  78  extend through the vertical side walls  67  of the conveyor housing  61 , adjacent to the bottom edge of the side wall  67 . Although seven conduit openings  78  are shown in each side wall  67 , it is understood that any desired number of the conduit openings  61  may be provided in each side wall  67 . An exhaust port  63 , provided with at least one exhaust fan  64 , is provided in the top  68  of the housing  61  for evacuating gas or air from the housing interior  62 , for purposes hereinafter described. An exhaust duct (not illustrated) typically conducts the gas or air from the exhaust port  63  to a suitable outlet.  
         [0035]    As illustrated in FIG. 8, the particle removing system  60  further includes a pair of purge gas delivery systems  70 , each of which is designed to distribute pressurized nitrogen gas or clean, dry air through the multiple conduit openings  78  in the corresponding side wall  67  of the conveyor housing  61 , and into the housing interior  67  thereof. Each purge gas delivery system  70  includes a conventional gas source  71  containing a supply of compressed nitrogen gas or clean, dry air. A central conduit  72  extends from fluid communication with the outlet of the gas source  71 , through one of the conduit openings  78  and terminates in the housing interior  62 . Multiple branch conduits  73  may extend from the central conduit  72  and through the remaining respective conduit openings  78 , where the branch conduits  73  likewise terminate in the housing interior  62 . Each of the conduits  72 ,  73  is hermetically sealed with respect to the edges of the respective conduit openings  
         [0036]    In an alternative embodiment (not shown), each of the conduits  72 ,  73  may have its own gas source  71 , or two, three or more of the conduits  72 ,  73  may extend from a common gas source  71 . Still further in the alternative, the conduits  72 ,  73  of both purge gas delivery systems  70  may be served by a common gas source  71 . It will be recognized by those skilled in the art that numerous variations in number and configuration for the gas source or sources  71  and the conduits  72 ,  73  may be made without departing from the spirit and scope of the invention.  
         [0037]    As further illustrated in FIGS. 7 and 8, a light emitter  83  and a light sensor  85  are provided on the side walls  67 , inside the housing interior  62  in aligned relationship to each other and just above the level of the conveyor belt  2 , adjacent to the entry end  65  of the housing  61 . An additional light emitter  86  and light sensor  87  pair are in like manner provided at the exit end  66  of the housing  61 . As illustrated in FIG. 8, each light sensor  85 ,  87  may be connected to a process controller  77  by means of sensor wiring  81 , which process controller  77  is connected to the operational components of each gas source  71  typically by means of additional wiring  79 , as illustrated schematically in FIG. 8. The process controller  77  may further be connected to the exhaust fans  64  of the exhaust port  63 , or alternatively, the exhaust port  63  may have its own separate control system. Accordingly, each light emitter  83 ,  86  continually emits a light beam  84  (FIG. 7) which is received by the corresponding aligned light sensor  85 ,  87 . As the conveyor belt  2  carries a pod  8  through the housing interior  62 , the pod  8  first interrups the light beam  84  of the emitter  83 /sensor  85  pair at the entry end  65  of the housing  61 , and this interruption is sensed by the light sensor  85 , which sends a signal to the process controller  77  to begin operation of the gas source or sources  71 . As it reaches the exit end  66  of the housing  61 , the pod  8  interrupts the light beam  84  of the emitter  86 /sensor  87  pair at the exit end  66  of the housing  61 , and the light sensor  87  sends a signal to the process controller  77  to terminate operation of the gas source or gas sources  71 . It will be understood that the present invention contemplates the use of any alternative type of sensor system known by those skilled in the art to detect the presence of the wafer pod  8  at the entry end  65  and the exit end  66  of the housing  61 .  
         [0038]    Referring again to FIGS. 6 and 7 of the drawings, in typical application of the stocker conveyor particle removing system  60 , a pod  8  containing semiconductor wafers (not illustrated) is transported from the output port of the station  4  to the input port of the stocker  6  for ultimate distribution to another location in the semiconductor production plant. After the pod  8  is loaded onto the conveyor belt  2  by means of conventional automated equipment (not illustrated) at the station  4 , the conveyor belt  8  carries the pod  8  into the housing interior  62  at the entry end  65  of the housing  61 . Accordingly, the pod  8  initially interrupts the light beam  84  emitted by the light emitter  83 , and the light sensor  85  senses the light interruption and sends the appropriate message to the process controller  77 . The process controller  77 , in turn, actuates the operating components of the gas source or sources  71 , which deliver nitrogen gas or clean, dry air typically at a pressure of about 80 p.s.i. through the central conduit  72  and branch conduits  73  and into the housing interior  62 . The process controller  77  may also actuate the exhaust fans  64  (FIG. 8) of the exhaust port  63 . Simultaneously, the exhaust port  63  draws the nitrogen gas or clean, dry air from the housing interior  62  to the exhaust duct (not illustrated). Consequently, a continuous gas or air flow pattern is established inside the housing interior  62 , between the high-pressure air or gas discharge ends of the conduits  72 ,  73  inside the housing interior  62  and the low-pressure exhaust port  63 . The flowing gas or air tends to remove dirt, dust and other potential wafer-contaminating particles from the top, front, rear, side and bottom surfaces of the pod  8  during transit of the pod  8  through the housing interior  62 , and discharges most or all of the particles with the air or gas through the exhaust port  63 . When the pod  8  reaches the light emitter  86 /light sensor  87  pair at the exit end  66  of the housing  61 , the pod  8  interrupts the light beam  84 , and the light sensor  87  sends the appropriate message to the process controller  77 , which terminates operation of the air or gas source or sources  71 , and the exhaust port  63 , if applicable. The pod  8  is finally delivered into the stocker  6  for sorting or temporary storage therein, in conventional fashion.  
         [0039]    Referring next to FIG. 9 of the drawings, another illustrative embodiment of the particle removing system of the present invention is generally indicated by reference numeral  88  and includes a conventional static electricity remover or ionizer  90 , mounted typically on the interior surface of the conveyor housing  61 , above or adjacent to the conveyor belt  2 . The ionizer  90  may be connected to the process controller  77 . Accordingly, upon entry of the wafer pod  8  into the housing interior  62 , the ionizer  90  may be operated to remove static electricity from the surfaces of the pod  8  and inhibit static electricity-induced clinging of particles to the pod  8  before the air- or gas-induced removal of the particles from the pod  8  as heretofore described.  
         [0040]    An alternative configuration for the conduits  72 ,  73  of the purge gas delivery system or systems  70  is illustrated in FIG. 10, wherein the discharge end of each conduit  72 ,  73 , instead of extending through the corresponding conduit opening  78  in the housing  61 , terminates immediately adjacent to the conduit opening  78 , outside the housing  61 . Air or gas flowing from the discharge ends of the respective conduits  72 ,  73  is thus drawn into the corresponding conduit opening  78  due to the air or gas pressure drop induced in the housing interior  62  by the exhaust port  63 .  
         [0041]    While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may 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.