Abstract:
A material handling system includes an overhead rack defining a plurality of storage positions. The overhead rack defines at least one interior window devoid of storage locations. First and second side rails are disposed above the overhead rack. A first cross rail is movably coupled to the first and second side rails. A first transport vehicle movably is coupled to the first cross rail and operable to descend below the overhead rack through the at least one interior window.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       BACKGROUND 
       [0002]    The disclosed subject matter relates generally to semiconductor manufacturing and, more particularly, to an overhead substrate handling and storage system. 
         [0003]    Growing technological requirements and the worldwide acceptance of sophisticated electronic devices have created an unprecedented demand for large-scale, complex, integrated circuits. Competition in the semiconductor industry requires that products be designed, manufactured, and marketed in the most efficient manner possible. This requires improvements in fabrication technology to keep pace with the rapid improvements in the electronics industry. Meeting these demands spawns many technological advances in materials and processing equipment and significantly increases the number of integrated circuit designs. These improvements also require effective utilization of computing resources and other highly sophisticated equipment to aid, not only design and fabrication, but also the scheduling, control, and automation of the manufacturing process. 
         [0004]    Turning first to fabrication, integrated circuits, or microchips, are manufactured from modern semiconductor devices containing numerous structures or features, typically the size of a few micrometers or less. The features are placed in localized areas of a semiconducting substrate, and are either conductive, non-conductive, or semi-conductive (i.e., rendered conductive in defined areas with dopants). The fabrication process generally involves processing a number of wafers through a series of fabrication tools. Each fabrication tool performs one or more of four basic operations discussed more fully below. The four basic operations are performed in accordance with an overall process to finally produce the finished semiconductor devices. 
         [0005]    Integrated circuits are manufactured from wafers of a semiconducting substrate material. Layers of materials are added, removed, and/or treated during fabrication to create the integrated, electrical circuits that make up the device. The fabrication essentially comprises the following four basic operations:
       layering, or adding thin layers of various materials to a wafer from which a semiconductor is produced;   patterning, or removing selected portions of added layers;   doping, or placing specific amounts of dopants in selected portions of the wafer through openings in the added layers; and   heat treating, or heating and cooling the materials to produce desired effects in the processed wafer.       
 
         [0010]    Although there are only four basic operations, they can be combined in hundreds of different ways, depending upon the particular fabrication process. 
         [0011]    To facilitate processing of wafers through a process flow, wafers are typically grouped into lots. Each lot is housed in a common wafer carrier. Carriers are transported to various process and metrology tools throughout the fabrication facility to allow the required processes to be completed to fabricate integrated circuit devices on the wafers. 
         [0012]    Modern wafer fabrication facilities employ automated material movement systems to satisfy ergonomic concerns and to maintain a high level of automation. Interbay/intrabay vehicle automated material handling systems may be employed to automate the transfer of wafers to the tools required in the process flow. One factor contributing to the efficiency of the material handling system is the delivery time between tools. Delivery time may vary depending on the distance between tools, the congestion of the tools, and the distance an idle material handling vehicle needs to travel to pick up a waiting wafer carrier. Delivery times directly affect tool utilization and system throughput. 
         [0013]    Due to the large number of substrates being fabricated concurrently, a large number of wafer carriers may be disposed in wafer storage areas, referred to as stockers, while they await further processing. The automated material handling system coordinates transfer of the carriers to and from the storage locations and between the various processing and metrology tools. Moves to and from storage interrupt the process flow of the substrates and also add to material handling system congestion and delay. 
         [0014]    This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
       BRIEF SUMMARY 
       [0015]    The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
         [0016]    One aspect of the disclosed subject matter is seen in a material handling system including an overhead rack defining a plurality of storage positions. The overhead rack defines at least one interior window devoid of storage locations. First and second side rails are disposed above the overhead rack. A cross rail is movably coupled to the first and second side rails. A first transport vehicle movably is coupled to the cross rail and operable to descend below the overhead rack through the at least one interior window. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    The disclosed subject matter will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0018]      FIGS. 1-3  are isometric views of a matric material handling system; 
           [0019]      FIG. 4  is a top view of the matrix material handling system of  FIG. 1 ; 
           [0020]      FIG. 5  is a top view of a matrix material handling vehicle in the system of  FIGS. 1-5 ; 
           [0021]      FIG. 6  is a diagram of a purge nest for controlling the environment of a wafer pod in the matrix material handling system of  FIGS. 1-5 ; and 
           [0022]      FIG. 7  is a cut-away side view of the matrix material handling system of  FIGS. 1-5 . 
       
    
    
       [0023]    While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosed subject matter as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0024]    One or more specific embodiments of the disclosed subject matter will be described below. It is specifically intended that the disclosed subject matter not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the disclosed subject matter unless explicitly indicated as being “critical” or “essential.” 
         [0025]    The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the disclosed subject matter with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
         [0026]    Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to  FIGS. 1-5 , the disclosed subject matter shall be described in the context of a matrix material handling system (MMHS)  100 .  FIGS. 1-3  are various isometric views of the MMHS  100 , and  FIG. 4  is a top view of the MMHS  100 . The MMHS  100  is disposed over a plurality of manufacturing tools  110 , such as tools used in the fabrication of semiconductor devices. In a semiconductor fabrication environment, exemplary manufacturing tools  110  include processing tools (e.g., photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal processing tools, implantation tools, etc.), metrology tools, sorters, etc. 
         [0027]    The particular tools  110  disposed below the MMHS  100 , and their arrangement may vary depending on the particular implementation and the processing steps being performed. In one example, tools  110  in a common tool family may be grouped in common control areas. Hence, photolithography tools may be located in one control area, while etch tools may be located in another control area. In another example, the tools  110  may be grouped by process layer. Hence, the tools required to form a particular layer (i.e., starting with a photolithography step and terminating prior to the next photolithography step) may be grouped into a common control area. 
         [0028]    The MMHS  100  includes one or more linear material handling vehicles  120  and one or more matrix material handling vehicles  130 . Generally, the linear material handling vehicles  120  move along overhead rails  140  disposed in aisles  150  between the tools  110 . An overhead rack  160  defines a plurality of storage positions  170  over the tools  110  for receiving wafer pods  180 . The linear material handling vehicles  120  move wafer pods  180  between different areas of a manufacturing facility, to one of the tools  110 , or to one of the storage positions  170  in the overhead rack  160 . For example, predefined input/output (I/O) port positions  190  may be defined along the periphery of the overhead rack  160  to receive or dispatch pods  180  from or to the overhead rack  160 . In one embodiment, an I/O port  190  may be provided on each side of the overhead rack  160 . 
         [0029]    The matrix material handling vehicles  130  move pods  180  to various positions within the overhead rack  160  or to one of the tools  110 . The matrix material handling vehicles  130  are movably coupled to a gantry drive system including side rails  200  and a cross rail  210 , as shown in  FIG. 5 . The cross rail  210  includes a drive mechanism for moving along the side rails  200 , and the matrix material handling vehicles  130  include a drive mechanism for moving along the cross rail  200  to access the various storage positions  170 . The linear material handling vehicles  120  and the matrix material handling vehicles  130  also include hoist systems for raising or lowering the pods  180  to engage the overhead rack  160  or to interface with a load port  220  of one of the tools  110 . 
         [0030]    Drive systems for moving the vehicles  120 ,  130  along the rails  140 ,  200 ,  210  and hoist systems for raising and lowering the pods  180  to interface with the overhead rack  160  or the tools  110  are known to those of ordinary skill in the art, so they are not described in greater detail herein to avoid obscuring the present subject matter. 
         [0031]    Certain storage positions  181  may be equipped with equipment to establish a vacuum and/or to provide nitrogen gas, extremely clean dry air (XCDA), or some other purge gas) for pods  180  stored therein. These pods  180  may be stored under protected conditions (e.g., to avoid oxidizing exposed regions of the wafers) near the tools  110  needed for the next process operation. This protected storage near the tool  110  increases throughput and yield. An exemplary storage location  181  equipped with a purge nest  182  is shown in  FIG. 6 . The purge nest  182  includes a frame  183  for supporting a wafer pod  180 . A purge port  184  fed by a gas supply line  185  is provided to supply a cover gas for the interfacing pod  180  (not shown). A vacuum port  186  coupled to a vacuum line  187  may be used to remove the purge gas exiting the pod  180 . 
         [0032]    The overhead rack  160  defines one or more interior windows  230  to allow a matrix material handling vehicle  130  to interface with a load port  240  of a tool not disposed along the periphery of the overhead rack  160  (i.e., along an aisle  150 ). The matrix material handling vehicle  130  may be provided with rotating grippers to allow a wafer pod  180  to be rotated as well as lowered, so that the pod  180  may be aligned at any angle (e.g., aligned with various cluster tool facets). The overhead rack  160  also defines periphery windows  250  to allow access to the aisle-oriented load ports  220 . 
         [0033]    The overhead rack  160  may be constructed of a plurality interlocking grid pieces that can be dynamically configured to arrange the windows  230  relative the load ports  240 . For tools  110  that are susceptible to particulate contamination (e.g., while they are opened during preventative maintenance procedures), a fan filter unit (FFU) containing a high efficiency particulate air (HEPA) filter may be mounted immediately beneath the overhead rack  160 . For tools  110  that have utilities or exhaust ducts passing through the ceiling, the utilities and exhaust may be grouped to penetrate an interior window  230  selectively placed in the matrix, or grouped adjacent to the overhead rack  160  so as to not inhibit the travel of the matrix material handling vehicles  130  over tool load ports  220 . 
         [0034]    Either the linear material handling vehicles  120  or the matrix material handling vehicles  130  can access the aisle-oriented load ports  220  to load the tools  110 . Generally, a linear material handling vehicle  120  lowers the pod  180  and reaches out to engage the load port  220 , while the matrix material handling vehicle  130  traverses through the periphery window  250  to engage the pod  180  with the load port  220 . 
         [0035]      FIG. 7  illustrates a cut-away side view of the MMHS  100  illustrating how tool density may be increased due to the overhead and matrix vehicles  120 ,  130 . In the embodiment illustrated in  FIG. 7 , the system  100  includes linear material handling vehicles  120 A-F and matrix material handling vehicles  130 A-B. The inside linear material handling vehicles  120 C,  120 D may be provided to allow traffic to bypass the illustrated portion of the MMHS  100 . The linear material handling vehicles  120 A,  120 B,  120 E,  120 F may be used to load tools  110 A-E or to transfer pods  180  in to and out of their respective portions of the overhead rack  160 A,  160 B. The tools  110 A-E may be arranged with load ports  220 A-D that are disposed on edges of the MMHS  100  and load ports  240 A,  240 B that are disposed not on the edges. Interior windows  235 A-B and periphery windows  250 A-D are provided to allow the matrix material handling vehicles  130 A-B to access the various load ports  220 A-D,  240 A-B. 
         [0036]    For example, the load port  220 A disposed along the edge may be accessed by the linear material handling vehicle  120 A or by the matrix material handling vehicle  130 A through the periphery window  250 A. The load port  240 A that is not disposed along the edge may be accessed by the matrix material handling vehicle  130 A through the interior window  235 A. The layout of the tools  110 A-E may be varied depending on the amount of available floor space and the size and port positions of the tools to improve the density of the layout. 
         [0037]    Because the matrix material handling vehicle  130  can interface with a tool  110  through an interior window  230 , the tools  110  need not be arranged in a completely linear fashion, as is the case in a conventional machine layout. Because the size and port orientation of the various tools  110  may vary, avoiding a linear layout allows a denser tool layout, thereby conserving floor plan space to increase fab capacity and reducing the traversal distance between tools  110  to increase throughput. Due to the number of storage positions  170  in the overhead rack  160  conventional stockers need not be provided in the MMHS  100 , thereby reducing overall system cost and increasing throughput by avoiding moves to and from the stockers. 
         [0038]    In one embodiment, the tools  110  disposed along the aisles  150  may be provided with conventional SEMI ports  240  for receiving conventional front opening unified pods (FOUP). These conventional ports  240  may be accessed by either the linear material handling vehicles  120  or the matrix material handling vehicles  130 . Tools  110  disposed near the interior windows  230  may be provided with advanced ports for receiving advanced wafer pods. For example, pods  180  may be provided that do not open to external atmosphere for loading or unloading. A protective gas may be provided during the transfer operation. The advanced load port may be provided for a cluster tool  110 , a carrier capable of directly interfacing with a vacuum, etc. The use of advanced pods allows direct process to process moves, which increased both yield and throughput. These direct moves also eliminates the need for FOUP handling steps, thereby reducing hardware requirements and improving cycle times. 
         [0039]    The overhead rack  160  may be shared by more than one matrix material handling vehicle  130 . For example, as shown in  FIG. 2 , four or more cross rails  200  may be provided over the rack  160 , each with its own matrix material handling vehicle  130 . Shared regions may be defined in the overhead rack  160  that can be accessed by different matrix material handling vehicles  130 . One matrix material handling vehicle  130  can place a pod  180  in a storage position  170  after processing by a tool  110 , and another matrix material handling vehicle  130  can retrieve the pod  180  at a later time to move it to a different tool  110  for the next operation. If one matrix material handling vehicle  130  fails, another matrix material handling vehicle  130  can bump the cross rail  200  out of the way to access storage positions  170  in the overhead rack  160  that had been serviced by the failed matrix material handling vehicle  130 . 
         [0040]    The MMHS  100  eliminates single points of failures because the overhead rack  160  can be loaded from by the linear material handling vehicles  120  using overhead rails  140  on either side. In cases where there is no failure, this effectively doubles the throughout density. Overlapping portions of the overhead rack  160  may be accessed by different matrix material handling vehicle  130 . The two-dimensional capabilities of the matrix material handling vehicles  130  also allow fast swapping at the tools  110  and access to tools  110  disposed beneath the overhead rack  160 . Traffic blockages associated with conventional linear material handling systems may be avoided due to the increased number of movement axes. 
         [0041]    The proximity of the overhead rack  160  to the tools  110  allows shared local buffering for tools  110  of the same type. Multiple pods  180  requiring the same operation may be stored proximate tools  110  of the same type without requiring the scheduling system to identify the particular tool  110  that will perform the next operation. The matrix material handling vehicles  130  may deliver the pod  180  to the selected tool  110  after the dispatch decision is made without incurring a material handling delay. Kits of test wafers may also be stored proximate to tools  110  where they may be employed (e.g., to qualify a tool after maintenance) to save cycle time and reduce material handling traffic. 
         [0042]    Scheduling for the MMHS  100  may be provided by centralized and local schedulers. A centralized scheduler schedules global moves within the system  100 , while local controllers control moves for pods  180  stored on the overhead rack  160  for a group of tools  110  to effect the processing of the wafers over a plurality of process steps. An exemplary scheduling system is described in U.S. patent application Ser. No. 13/247,792, entitled “Methods and Systems for Semiconductor Fabrication with Local Processing Management”, and incorporated herein by reference in its entirety. 
         [0043]    The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.