Patent Publication Number: US-7217076-B2

Title: Semiconductor material handling system

Description:
CLAIM OF PRIORITY 
     This application claims priority from provisional application entitled “UNIVERSAL MODULAR PROCESSING INTERFACE SYSTEM”, Application No. 60/316,722, filed Aug. 31, 2001, and which application is incorporated herein by reference. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     1. U.S. patent application Ser. No. 10/087,400, entitled “Wafer Engine,” which was filed with the U.S. Patent and Trademark Office on Mar. 1, 2002; 
     1. U.S. patent application Ser. No. 10/087,638, entitled “Unified Frame for Semiconductor Material Handling System,” which was filed with the U.S. Patent and Trademark Office on Mar. 1, 2002; and 
     1. U.S. patent application Ser. No. 10/234,640 entitled “Universal Modular Wafer Transport System,” which was filed with the U.S. Patent and Trademark Office on Sep. 3, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to a wafer transfer system. More particularly, the present invention is a unified, scalable frame or structure that equipment front end module (EFEM) components mount to, and wafer engine for transferring wafers. 
     BACKGROUND OF THE INVENTION 
     Standard Mechanical Interface Pods (SMIF pods) are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which wafers may be stored and transferred. One type of pod is a front opening unified pod, referred to as FOUP  10 , in which the pod door is located in a vertical plane, and the wafers are supported either in a cassette mounted within the pod shell, or two shells mounted in the pod shell. 
     During the fabrication of semiconductor wafers, the SMIF pods are used to transport the workpieces between various tools in the wafer fab. These tools include process tools for forming integrated circuit patterns on the wafers, metrology tools for testing the wafers, sorters for sorting and rearranging the wafers within one or more SMIF pods, and stockers for large scale storage of SMIF pods. The tools are generally laid out in a wafer fab in one of two configurations, a bay and a chase configuration or a ballroom configuration. In the former arrangement, only the front of the tool including the workpiece I/O port is maintained in the clean room environment of Class-1 or better. In the ballroom configuration, the tools are arranged in clusters according to the operations they perform, with the entire tool being maintained in the clean room environment of Class-1 or better. 
     Tools within a wafer fab include a front-end interface which houses components that facilitate and monitor the transfer of workpieces (i.e. wafers) between the pods to the tools. A conventional front end unit or equipment front end module (EFEM)  20  is shown in  FIGS. 1–2 . EFEMs  20  are generally constructed at a tool manufacturer and then shipped to a wafer fab. 
     An EFEM  20  generally includes a housing  22  which is fixed to the front of the tool and a workpiece handling robot  24  mounted within the housing and is capable of x, r, θ, Z motion to transfer workpieces between the workpiece carriers, tool and other front end components. The robot  24  is generally mounted with leveling screws that will allow the adjustment of the planarity of the robot  24  once the EFEM  20  is constructed and affixed to a tool. 
     In addition to a robot  24 , the EFEM  20  generally includes one or more prealigners  26  for performing the operation of wafer center identification, notch orientation, and indocile mark reading. The prealigner(s)  26  are commonly bolted into the housing  22  with leveling screws allowing the planarity of the prealigner(s) to be adjusted once the EFEM  20  is constructed and affixed to a tool. 
     An EFEM  20  further includes one or more load port assemblies  28  for receiving a workpiece carrier, opening the carrier, and presenting the workpiece to the robot  24  for transfer of the workpieces between the carrier, and other processing tools. For 300 mm wafer processing, a vertically oriented frame, commonly referred to as a Box Opener-Loader Tool Standard Interface (or “BOLTS” interface), has been developed by Semiconductor Equipment and Materials International (“SEMI”) . The BOLTS interface attaches to, or is formed as part of, the front end of a tool, and provides standard mounting points for the load port assembly to attach to the tool. U.S. Pat. No. 6,138,721, entitled “Tilt and Go Load Port Interface Alignment System,” which is assigned to the owner of the present application and which is incorporated by reference in its entirety herein, discloses a system for adjusting a load port assembly to the proper position adjacent a BOLTS interface and then affixing the load port assembly to the interface. 
     Once the robot  24 , the prealigners  26  and load port assemblies  28  have been mounted to the housing  22 , the EFEM  20  is shipped to the wafer fab and affixed to a tool within the fab. After being properly secured to the tool, the EFEM components are leveled within the housing  22  via the leveling screws, and the robot  24  is then taught the acquisition and drop-off positions it will need to access for workpiece transfer between the load port assemblies, the prealigners and the tool. A system for teaching the various acquisition and drop-off positions for the robot within the tool front end is disclosed in U.S. patent application Ser. No. 09/729,463, entitled “Self Teaching Robot,” which application is assigned to the owner of the present application and which application is incorporated by reference herein in its entirety. Once the robot positions have been taught, side panels are attached to housing  22  to substantially seal the housing against the surrounding environment. 
     For example, conventional EFEMs include many separate and independent workpiece handling components mounted within an assembled housing. The housing  22  includes a structural frame, bolted, constructed or welded together, in a plurality of panels affixed to the frame. After the housing  22  is assembled, the EFEM components are fixed to the various panels. It is a disadvantage to prior art EFEMs that the overall system tolerances are compounded with each frame member, panel and component connection. The result is that the assembled EFEM components are poorly aligned and need to be adjusted to the proper position with respect to each other. The robot  24  must also be taught the relative positions of the components so that the EFEM components can interact with each other. This alignment and teaching process must take place every time there is an adjustment to one or more of the EFEM components. 
     A further shortcoming of the prior art is that EFEM components are frequently made by different suppliers, each with its own controller and communication protocols. Steps must be taken upon assembly of the EFEM so that the controllers of each component can communicate with each other and the components can interact with each other. The separate controllers also complicate maintenance and add to the parts and electrical connections provided in the EFEM. Further still, especially in a ballroom configuration, the conventional EFEM takes up a large amount of space within a Class-1 cleanroom environment where space is at a premium. 
     Today&#39;s 300 mm semiconductor EFEMs are comprised of several major subsystems including SEMI E15.1 compliant load port modules (typically 2–4 per tool). For example, an EFEM may consist of a wafer handling robot and a fan filter unit mounted to a structural steel frame, and have panels to enclose the wafer handling area between the load ports and the process tool. The combination of these components provides a means of transferring wafers to and from a FOUP  10 , and between the FOUP and the process tool wafer dock(s). FOUPs  10  are manually loaded via operators or automatically loaded via an automated material handling system (AMHS) delivered to and taken from the Load Port. Industry Standards have been created to allow multiple vendors to provide the Load Port, FOUP  10 , or other EFEM components to be integrated as a system. 
     The Load Port component provides a standard interface between the AMHS and the wafer handling robot in the EFEM. It provides a standardized location to set the FOUP  10 , docks the FOUP  10  to seal the front surface, and opens and closes the door to allow access to the wafers in the FOUP  10 . The dimensions of this unit are all specified in SEMI E15.1. 
     The Load Port attaches to the Front End via the Bolts Interface which is defined by SEMI E-63. This standard defines a surface and mounting holes to which the Load Port attaches. It is defined to start at the fab floor and goes as high as 1386 mm from the floor and is about 505 mm wide per Load Port. As a result, the load port completely blocks off the process tool from the operator aisle in the fab. SEMI E-63 also defines load port dimensions on the tool side to ensure interchangeability with a variety of robot manufacturers. 
     The primary functions of the load port include accepting a FOUP  10  from and presenting to a FOUP  10  to the Fab AMHS, moving the FOUP  10  towards and away from the port seal surface (docking/undocking), and opening and closing the FOUP door. In addition, it must perform functions such as locking the FOUP  10  to the advance plate, lock and unlock the FOUP door, and a variety of lot ID and communication functions. Per SEMI E15.1, all of these functions are contained in a single monolithic assembly which is typically added or removed from the tool front end as a complete unit. 
     The load port must be aligned with precision to the wafer robot. If there are multiple load ports in the system, they must all present the wafers in level parallel planes. Typically, the Load Ports provide several adjustments to planarize the wafer in the FOUP  10  with the robot. In order to minimize time spent calibrating the robot to each of the 25 wafer positions in each of the FOUPs  10 , specialized tools and alignment fixtures are used in conjunction with all of the adjustments. If a load port is swapped out with a new one, the calibration procedure can be quite lengthy. 
     In addition to aligning the robot to the wafers positions, the door mechanism must also be aligned with the door opening and the door seal frame. Again, this is typically performed with alignment fixtures and tools either on the tool front end or off line. 
     The robot must also be leveled and aligned with one or more tool drop off point. This is typically done manually by teaching the robot the position and making planarity adjustments either on the front end or the tool. 
     It is the combination of all of these relationships between the tool, the robot, and the FOUPs  10  which make setting up a tool front end so time consuming. All of the components are typically attached to a relatively low precision frame, and adjustments are used to compensate for it. The load ports are mounted to the front surface, the robot to the base, the fan/filter unit (FFU) to the top, and skins on all other open surfaces to complete the mini-environment enclosure. 
     It would be advantageous to minimize the adjustments between the components and reduce the overall time required to align the load port. The present invention provides such an advantage. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to provide a unified structure or frame that precisely ties many critical EFEM components together. In one embodiment, the frame serves as a single reference for aligning the interior and exterior EFEM components. In another embodiment, the interior and exterior EFEM components are aligned in relation to each vertical strut of the frame. 
     Another aspect of the present invention is to provide a unified structure or frame that is scalable in size. In one embodiment, the unified structure includes vertical struts secured to an upper and lower support member. The number of vertical struts and the length of the upper and lower support member depends on the number of I/O ports within the EFEM. Similarly, the size and spacing of the vertical struts and the support members may vary to accommodate 200 mm wafers, 300 mm wafers, and 400 mm wafers. 
     Yet another aspect of the present invention is to accurately and precisely locate the front load components with respect to each other. Preferably, this calibration process is accomplished with a minimum number of adjustments. In one embodiment, all the interior and exterior EFEM components are precisely tied to the unified frame such that they share common reference points. 
     Yet another aspect of the present invention is to provide a unified frame that segregates and isolates the port door/carrier door assembly from the many of the interior EFEM components. In one embodiment, the port door/carrier door assembly is lowered into a separate air flow/storage area located within the mini-environment. The storage area prevents particles created by, for example, a wafer handling robot, from contaminating the assembly. 
     Still another aspect of the present invention is to provide a wafer carrier docking/interface plate that can be easily removed from the EFEM to access the interior of the EFEM. In one embodiment of the present invention, the removable plate is manufactured from a transparent material so that a user may observe any problems/malfunctions that occur within the mini-environment. 
     Still another aspect of the present invention is to decrease the footprint of the EFEM. In one embodiment, the EFEM is supported by a rolling stand whereby the bottom surface of the EFEM is raised off the floor of the wafer fab. The area between the wafer fab floor and the EFEM may serve as a maintenance access port to the processing tool, or an area to place auxiliary compartments. 
     Still another aspect of the present invention is to provide a wafer engine for transferring wafers. In one embodiment, the wafer engine may perform a number of inspection, marking, and metrology functions, eliminating the need for a separate processing station. 
     Still another aspect of the present invention is to provide a wafer engine that may transfer wafers within the reduced footprint of the EFEM. In one embodiment, a wafer engine includes a linear drive for moving the wafer along a x-axis, a vertical drive for moving the wafer z-axis, a radial drive for moving the wafer along a radial axis, and a rotational drive for rotating the vertical and radial drive about a theta axis. 
     A further aspect of the present invention is to provide local filtering for various particle generating mechanisms on the wafer engine. In one embodiment, a fan/filter unit is mounted to the radial drive to capture particles created by the radial drive. In another embodiment, an exhaust system creates an air flow through the vertical drive to capture any particles created by the vertical drive. These localized fan/filter units attempt to control particles created by the wafer engine by exhausting the particles into a “dirty-air” environment, or by first filtering the air before it is exhausted back into a “clean air” environment. 
     Still another aspect of the present invention is to provide a wafer engine that has dual swap and align-on-the-fly capabilities. In one embodiment, the wafer engine has a rapid swap radial drive, or buffer capability, to simultaneously store and transfer two wafers. In another embodiment, an upper end effector may rotate and align a first wafer while a second wafer is stored and/or transported by a lower end effector. 
     Still another aspect of the present invention is to provide a wafer engine that has a removable/interchangeable slide body mechanism. In one embodiment, the slide body mechanism includes integrated processing tools such as an OCR reader, an aligner, an ID reader, or a metrology tool. A removable slide body mechanism allows a wafer fab to incorporate the same wafer engine throughout whereby only the slide body mechanism must be customized to each individual process station. 
     Yet another aspect of the present invention is to provide a wafer engine having a vertical drive located above the theta drive. Such a vertical drive is located substantially within the FOUP  10  area and minimizes the footprint of the wafer engine. 
     The present invention provides all of these advantages. 
    
    
     
       DETAILED DRAWINGS OF THE PRESENT INVENTION 
         FIG. 1  is a perspective view of a conventional front end assembly in accordance with the prior art; 
         FIG. 2  is a top view of the front end assembly shown in  FIG. 1 ; 
         FIG. 3  is a side view of a conventional front end assembly in accordance with the prior art; 
         FIG. 4  is a perspective view of an embodiment of the spine structure, according to the present invention; 
         FIG. 5  is a partial exploded view of the spine structure shown in  FIG. 4 ; 
         FIG. 6  is a perspective view of an embodiment of a FOUP docking interface, according to the present invention; 
         FIG. 7  is a partial exploded perspective view of an embodiment of the spine structure and front end load components, according to the present invention; 
         FIG. 8  is a perspective view of an embodiment of a wafer engine mounted to the spine structure, according to the present invention; 
         FIG. 9  is a perspective view of an embodiment of a wafer engine drive rail mounted to the spine structure, according to the present invention; 
         FIG. 10  is a side view of an embodiment of the front end load interface, according to the present invention; 
         FIG. 11  is a partial exploded view of another embodiment of the integrated mini-environment and structure, according to the present invention; 
         FIG. 12  is a side view of the integrated mini-environment and structure as shown in  FIG. 11 ; 
         FIG. 13  is a partial perspective view of an embodiment of the backbone structure according to the present invention; 
         FIG. 14  is perspective view of still another embodiment of the integrated mini-environment and structure, according to the present invention; 
         FIG. 15  is an end view of the integrated mini-environment and structure shown in  FIG. 14 ; 
         FIG. 16  is a partial exploded view illustrating an embodiment of the unitized frame of the integrated mini-environment and structure shown in  FIG. 15 ; 
         FIGS. 17A–17B ;  FIG. 17A  is a top view of an embodiment of a conventional wafer handling robot;  FIG. 17B  is a top view of the wafer handling robot shown in  FIG. 17A  with the end effector extended, according to the prior art; 
         FIG. 18  is a perspective view of an embodiment of a rapid swap wafer engine, according to the present invention; 
         FIG. 19  is a perspective view of the wafer engine shown in  FIG. 18  illustrating several of the components of the drive mechanisms and the vertical column and the slide body mechanism; 
         FIG. 20  is a perspective view of another embodiment of a wafer engine, according to the present invention; 
         FIG. 21  is a perspective view of the wafer engine shown in  FIG. 18 , illustrating the air flows created by the fan/filter units; 
         FIGS. 22A–22D ;  FIG. 22A  is a perspective view of still another embodiment of a wafer engine equipped with a wheeled aligner and an ID reader on the slide body mechanism, according to the present invention;  FIG. 22B  is a top view of the wafer engine shown in  FIG. 22A ;  FIG. 22C  is a slide view of the wafer engine shown in  FIG. 22A ;  FIG. 22D  is a rear view of the wafer engine shown in  FIG. 22A ; 
         FIG. 23  is a perspective view of an embodiment of the upper end effector shown in  FIG. 22A ; 
         FIGS. 24A–24C ;  FIG. 24A  is a cut away view of an embodiment of the wheeled end effector aligner illustrating a wafer supported by the pad;  FIG. 24B  is cut away view of the wheeled end effector aligner in  FIG. 24A  illustrating the wafer lifted off the pad and supported by the wheel;  FIG. 24C  is cut away view of the wheeled end effector aligner shown in  FIG. 24A  illustrating the wafer being released by the wheel and set back down on the pad; 
         FIG. 25  is a perspective view of yet another embodiment of the wafer engine, according to the present invention; 
         FIG. 26A–26B ;  FIG. 26A  is a perspective view of another embodiment of the radial drive;  FIG. 26B  is still another embodiment of the radial drive; 
         FIGS. 27A–27B ;  FIG. 27A  is a plan view illustrating the reach and swing clearance advantage of the wafer engine according to the present invention;  FIG. 27B  is plan view of a conventional linear slide robot illustrating the minimum clearance and maximum reach required; 
         FIG. 28  illustrates an example motion sequence for the rapid swap slide body with off center rotation axis, according to the present invention; 
         FIGS. 29A–29D ;  FIG. 29A  is a perspective view of an embodiment of the front end load interface, according to the present invention;  FIG. 29B  is a front view of the integrated system shown in  FIG. 29A ;  FIG. 29C  is a side view of an embodiment of the front end load interface shown in  FIG. 29A ;  FIG. 29D  is a plan view of an embodiment of the front end load interface shown in  FIG. 29A ; 
         FIGS. 30A–30B ;  FIG. 30A  is a perspective view of an embodiment of the integrated system mounted to a processing tool;  FIG. 30B  is a side view of the integrated system shown in  FIG. 30A ; and 
         FIG. 31  is a side view of the integrated system shown in  FIGS. 30A–30B , illustrating how the integrated system frees up space for Automated Material Handling System (AMHS) buffering. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     The present invention will now be described with reference to  FIGS. 4–31 , which relate generally to a wafer transfer system. The preferred embodiments of the present invention are used for 300 mm semiconductor wafer fabrication. The present invention may also be used in the fabrication of workpieces other than semiconductor wafers, such as for example reticles, flat paneled displays and magnetic storage disks. The present invention may also be used in the fabrication of workpieces larger or smaller than 300 mm, such as for example 200 mm and 150 mm. Moreover, while the present invention preferably operates within a FOUP system, it is understood that the present invention may operate with other workpiece transport systems, including open wafer cassette systems. 
     Unified Spine Structure 
     The spine structure  100  is based off the idea that a single unified frame or structure may serve as a base foundation for an EFEM. This foundation may be repeatedly manufactured in a similar fashion so as to lower the cost of the system, and allow EFEM components to mount to the frame to simplify alignment. The structure or frame  100  minimizes the amount of space required by a front end load tool. A frame or structure also minimizes alignment time and greatly simplifies access to components located inside the front end tool for maintenance procedures and/or services that are required. 
       FIGS. 4–5  illustrate a preferred embodiment of the unified spine structure  100 . The spine  100  includes multiple vertical struts  102  that are connected together by an upper channel or support member  104  and a lower channel or support member  106 . Each vertical strut  102  has an inward face  108  and an outward face  110 . As shown throughout  FIGS. 4–10 , each vertical strut  102  preferably has a substantially rectangular cross-section. A rectangular cross section is preferred so that the outward face  110  of each vertical strut  102  forms a seal with any EFEM component mounted to the vertical strut  102 . The rectangular cross-section of each vertical strut  102  also ensures that the upper support member  104  and lower support member  106  are flush against the inward face  108  and outward face  110  when secured to each vertical strut  102 . It is within the scope and spirit of the invention for the vertical strut  102  to have a different cross section such as, but not limited to, circular or oval. 
     In the preferred embodiment, the spine structure  100  is comprised primarily of sheet metal components, with a few machine components where the precision is required. The sheet metal is implemented in ways which take advantage of the precision that can be derived from some aspects of this fabrication technique. For example, the long bends in the upper support member  104  and lower support member  106  that form a “U”-shape provide a very straight reference to align the vertical struts  102 . In a preferred embodiment, holes  120  and  122  are punched in the upper and lower channel  104  and  106  to further guarantee good hole to hole alignment between each vertical strut  102  and the upper and lower channel  104  and  106 . 
     The sheet metal components also serve the function of exterior skins or mounting surfaces (described hereinafter) to the system as well as structural support. In current EFEM systems, sheet metal is usually reserved for non-structural panels which only provide cosmetic finish and containment. By incorporating sheet metal into several of the structural components, the material cost of the EFEM may be dramatically reduced. 
     The upper support member  104  is secured to the top portion  114  of each vertical strut  102 , while the lower support member  106  is secured to the bottom portion  112  of each vertical strut  102 . Accordingly, the spine  100  provides a very straight and stiff structure in both torsion and bending to build a front end load system on. In a preferred embodiment, the upper support member  104  and the lower support member  106  are manufactured from a single piece of sheet metal. The bends in the sheet metal to create the upper support member  104  are dictated by the width of the upper portion  114  of each vertical strut  102 , so that the width of the “U”-shaped upper support member  104  is substantially similar to the width of the upper portion  114  of each vertical strut  102 . Similarly, the width of the lower “U”-shaped support member  106  is preferably substantially similar to the width of the bottom portion  112  of each vertical strut  102 . Each support member  104  and  106  is intended to be flush against the inward face  108  and outward face  110  of each vertical strut  102 . 
     In a preferred embodiment, the lower portion  112  of each vertical strut  102  is wider than the upper portion  114  of each vertical strut  102 . As best shown in  FIGS. 4–5 , the spine structure  100  aligns each vertical strut  102  in a vertical orientation so that each vertical strut  102  is substantially parallel to each other. Each strut  102  is preferably spaced on 505 mm centers, which is the minimum allowed spacing for adjacent load ports per SEMI E-15.1. It is within the scope and spirit of the invention for the vertical struts  102  to be spaced apart at various or unequal distances. 
     To provide a rigid structure in both a torsional and lateral direction, each vertical strut  102  is secured to both the upper support member  104  and the lower support member  106 . Each vertical strut  102  is positioned between the upper support member  104  and lower support member  106  as shown in  FIG. 4 . As previously described, each vertical strut  102  is aligned with the mounting holes  120  and  122  in the upper support member  104  and the lower support member  106 . By way of example only, each vertical strut  102  is secured to the upper support member  104  by a bolt or pin secured to the top portion  114  of the vertical strut  102  (e.g. through mounting hole  120 ), and at least one bolt or pin secured to the front face  110  or the back face  108 . Each vertical strut  102  must also be secured to the lower support member  106 . By way of example only, a bolt or pin is secured to the bottom portion  112  of each vertical strut  102  (e.g. through mounting hole  122 ), and at least one bolt or pin is secured to both the front face  110  and the rear face  108 . 
     The “U”-shaped configuration of the upper support member  104  and the lower support member  106  further prevent each vertical strut  102  from rotating in place. Although the upper channel  104  and lower channel  106  as shown in  FIGS. 4–5  are manufactured from a single piece of sheet metal, it is within the scope and spirit of the invention for the upper support member  104  and lower support member  106  to be manufactured from multiple pieces of material. In a preferred embodiment, and as best shown in  FIG. 5 , the upper support member  104  and lower support member  106  have a perforated surface. The perforated surfaces of the upper support member  104  and lower support member  106  allow air from a fan/filter unit  150  (FFU) to flow through (see  FIG. 10 ). 
     When the lower support member  106  is secured to the vertical struts  102  it forms a front mounting surface  118  and a rear mounting surface  116  that various EFEM components may mount to (see  FIGS. 6–10 ). In general, the spine  100  creates at least three parallel and co-linear mounting surfaces: the front face  110  of the upper portion  112 , the front mounting surface  118 , and the rear mounting surface  116 . As will be described later, the EFEM components mount to one of these three surfaces. These three surfaces have a known spacial relationship between them, and thus components mounted to these surfaces may be aligned with minimal adjustments, or require no adjustments at all. 
     The lower support member  106  also creates an air flow area  121  located between the front mounting surface  118  and the rear mounting surface  116 . The air flow area  121  is designed to accommodate a FOUP door open/close module  139  that has been guided away from the port door opening and lowered down into the air flow area  121 . 
     Isolating the FOUP door open/close module  139  from the area the wafer engine  300  operates within has many advantages. For example, a single airflow generated by an FFU  150  is divided into two isolated air flows. One air flow will be directed towards the FOUP door open/close module  139 , while a second separate air stream will be directed into the wafer engine area. The two isolated air flows will provide a cleaner environment for the FOUP/port door assembly  139  than if a single air flow was circulated for both the wafer engine area and the FOUP door open/close module  139 . If there was only a single air flow path for both the wafer engine  300  and the FOUP assembly  130  particles created by the wafer engine,  300  may contaminate the FOUP/pod door assembly  139 . 
     The rear mounting surface  116  of the lower support member  106  also operates as a protective barrier between the FOUP door open/close module  139  and the wafer engine area. The rear mounting surface  116  prevents particles generated by the wafer engine  300  from entering the air flow area  121  storing the FOUP door open/close module  139 . The rear mounting surface  116  also allows the wafer engine  300  to have localized filtering and exhaust systems that exhaust “dirty” air containing particles below the wafer plane while not contaminate the FOUP door open/close module  139  (described hereinafter). 
     The spine structure  100  as shown in  FIGS. 4–5  is configured as a four FOUP I/O port EFEM. It is within the spirit and scope of the invention for the EFEM to include any number of I/O ports. Additionally, the EFEM may include spaces or blank I/O ports located between each I/O port that wafers will be transported through. As previously mentioned, the spine structure  100  is scalable. The number of vertical struts  102 , and the length of the upper support member  104  and the lower support member  106  may be modified to match the I/O port configuration required for the EFEM. 
     Each vertical strut  102  also has a cam guide  124  machined into the side surface. The cam  124  operates as a track or channel for guiding the FOUP door open/close module  139  rearward away from the FOUP  10  and subsequently downward into the air flow area  121 . The movement of the port/pod door assembly  139  may be controlled by a motor assembly (shown enclosed in a motor assembly housing  125  in  FIG. 7 ) located within the processing station. Such a motor assembly is known in the art and does not require further disclosure. It is within the scope and spirit of the invention to mechanically guide and move the FOUP door  12  and port door  140  into the storage area  121 . 
     The FOUP docking interface shown in  FIGS. 6–7  illustrate several EFEM components mounted to the spine structure  100 . By way of example only, the components may include a wafer engine or robot  300 , a FOUP support assembly  130 , a FOUP docking/isolation plate  138 , and a port door  140 . The FOUP support assembly  130  includes a FOUP advance support  132 , a FOUP advance module  133 , and a FOUP support plate  134 . 
     In order to transfer the workpieces from the FOUP  10  into the mini-environment (see FIG.  10 —“Class-1 Area”) a FOUP  10  is manually or automatedly loaded onto the port advance plate  134  so that the FOUP door faces the load port door  140 . A conventional load port door  140  includes a pair of latch keys which are received in a corresponding pair of slots in the door latching assembly mounted within the FOUP door. An example of a door latch within a FOUP door adapted to receive an operate with such latch keys is disclosed in U.S. Pat. No. 6,188,323, entitled “WAFER MAPPING SYSTEM,” issued to Rosenquiest et al., which patent is assigned to the owner of the present invention, in which patent is incorporated by reference herein in its entirety. In addition to decoupling the FOUP door from the FOUP shell, rotation of the latch keys also lock the keys into their respective FOUP door slots. There are typically two latch key and slot pairs, each of which pairs are structurally and operationally identical to each other. 
     A pod advance plate  134  typically includes three kinematic pins  135 , or some other registration feature, which mate within corresponding slots on the bottom surface of the FOUP  10  to define a fixed and repeatable position of the bottom surface of the FOUP  10  on the advanced plate  134 . Once a FOUP  10  is detected on the pod advanced plate  134 , the FOUP  10  is advanced toward the port door  140  until the FOUP door lies in contact with or is near the port door  140 . It is desirable to bring the front surfaces of the respective doors into contact with each other to trap particulates and to insure a tight fit of the port door latch key in the FOUP door key slot. U.S. patent application Ser. No. 09/115,414, entitled “POD DOOR TO PORT DOOR RETENTION SYSTEM,” by Rosenquist et al., and U.S. patent application Ser. No. 09/130,254, entitled “POD TO PORT DOOR RETENTION AND EVACUATION SYSTEM,” by Fosnight et al. disclose systems insuring a tight, clean interface between the FOUP  10  and port doors. These applications are assigned to the owner of the present invention, and are both incorporated by reference herein in their entirety. 
     Once the FOUP  10  and port doors are coupled, linear and/or rotational drives within the EFEM move the FOUP  10  and port doors together into the interior of the EFEM, and then away from the load port opening so that the workpieces may thereafter be accessible to the wafer engine  300 . As shown in  FIG. 10 , the port door  140  is affixed to the FOUP door and a controller actuates a slide to translate the carrier and port doors along the cam  124  located in each vertical strut  102 . The cam  124  guides the interlocked carrier and port doors vertically down into the air flow area  121  of the lower support member  106 . As previously mentioned, the port door  140  and FOUP door are isolated from the rest of the Class-1 area while stored in the air flow area  121 . The linear slide and rotational drive configurations (not shown) are known in the art and do not require further disclosure. A linear slide may be comprised of a linear bearing and a drive mechanism. By way of example only, the linear bearing may include a ball or air bearing. Similarly, the drive mechanism may include a motor with a cam lead screw, a belt drive, or a linear motor. The rotational drive may be comprised of, by way of example only, a gear motor, a direct drive, a belt drive, or other similar means. 
     After the FOUP  10  and port doors are moved away from the docking/isolation plate  138 , the wafer engine or robot  300  may transfer workpieces into the tool front end without interference from the stored FOUP  10  and port doors. Once operations on a workpiece lot at the tool have been completed and the workpieces have been returned to the FOUP  10 , the controller again actuates the drive and the slide to move the doors back into the I/O port, where upon the FOUP door is transferred and secured to the FOUP  10 . 
     The docking/isolation plate  138  is mounted to the front face  110  of each vertical strut  102 . The docking/isolation plate  138  isolates the interior region (Class-1 or “clean” area) of the tool front end from the outside ambient or exterior region. The docking/isolation plate  138  also provides an interface plane that the FOUP  10  is advanced towards to a close and controllable proximity (e.g., 0–5 mm separation). The plate  138  forms an auxiliary seal with the FOUP  10  and the port door  140 . An auxiliary seal allows a separation to exist between the plate  138  and the FOUP  10 , but still creates an airtight seal between the plate  138  and the FOUP  10 . An airtight seal between the plate  138  and the FOUP  10  is desirable to prevent gas from leaking out of the Class-1 Area or to maintain the inert environment of the load port interface. 
     The docking/isolation  138  is preferably manufactured from a single piece of material that includes one or more FOUP openings machined into it. The docking/isolation plate  138  includes registration holes  144  to locate it accurately with respect to each vertical strut  102 . This provides a machined, precision relationship between all the FOUP  10  openings for the EFEM. The docking/isolation plate  138  may also comprise individual pieces of material that mount to each vertical strut  102  using the same reference features. The plate  138  may be fabricated from materials such as, but not limited to, plastic, metal, sheet metal, or even glass. 
     In a preferred embodiment, the docking/isolation plate  138  is machined from a clear material, such as polycarbonate. Machining the docking/isolation plate  138  from a clear material provides an added benefit of being able to see inside the mini-environment or Class-1 Area while the tool is in operation. The current E15 load port/SEMI E63 Bolts Interface does not define this feature. The docking/isolation plate  138  does not have any structural features and therefore may be secured to each vertical strut  100  of the spine  100  by only a few bolts and/or pins. Thus, the docking/isolation plate  138  may be easily removed. Further, since none of the EFEM components align with reference to the docking/isolation plate  138 , the docking/isolation plate  138  maybe removed from the EFEM without disturbing the set up or alignment of the EFEM components such as the port door  140 , the FOUP advance plate  134 , or the wafer engine  300 . This provides a simple method of gaining access to the “clean” area (Class-1 area in  FIG. 10 ) of the EFEM for service, maintenance, or error recovery. 
       FIG. 8  illustrates the wafer engine  300  mounted to the spine structure  100 . From this view, it is clearly shown that the wafer engine  300  may travel linearly to access all the I/O ports of the EFEM. The wafer engine  300  travels along a rail assembly  302 , which is mounted to the rear mounting surface  116  of the lower support member  106 . In this embodiment, the linear drive  302  is shown as a belt drive. It is within the scope and spirit of the invention for the linear drive  302  to comprise other drive systems such as, but not limited to, a direct drive, a linear motor, a cable drive, or a chain link drive. The components of the wafer engine  300  will be described later. Such drive systems are well known in the art and do not require further disclosure. 
       FIG. 9  illustrates further detail of the rail system  302  shown in  FIG. 8  mounted to the spine structure  100 . The rail system  302  includes an upper x rail  310 , a lower x rail  312 , and a carriage guide  311 , all mounted to the rear mounting plate  118  of the lower channel  106 . In a preferred embodiment, the upper x rail  310  and the lower x rail  312  are circular or tubular, and are substantially parallel to each other. Engaging the upper x-rail  310 , the lower x-rail  312 , and the carriage guide  311  is an x carriage  304 . The upper and lower x rail  310  and  312  also serve as the main support for the wafer engine  300 . 
       FIG. 9  also illustrates a control box  147  that is preferably located below the FOUP advance assembly  130 . The EFEM requires many electrical control devices (e.g., control wiring, PCBs, etc.). It would be an advantage if these devices were easily accessible for maintenance and repair. The control box  147  provides an area to mount the electrical devices. In a preferred embodiment, the control box  147  has a pivoting front cover that may drop down for access to the electrical components inside. Within the control box are located many of the electrical components and control systems required to power and operate the EFEM components. It is intended that these electrical components may be easily accessed for maintenance purposes and therefore the pivoting front cover of the control box  147  is secured by a few bolts and/or pins that may be removed and allow the front cover to pivot downwards towards the floor of the fab. 
     As shown in  FIGS. 10 , and  30 – 31 , the spine structure  100  architecture provides a way to minimize the footprint of the EFEM and seal the clean volume of the system while still maintaining overall system accuracy. The FFU  150  mounts to and seals with the upper channel  104  and a tool interface panel  154  to form the top of the EFEM. The front seal is provided by mounting the docking/isolation plate  138  to the front face  110  of each vertical strut  102 . A sheet metal panel  152 , which is preferably a perforated surface, mounts to the lower support member  106  to form the bottom of the EFEM. The panel  152  also acts as an exhaust plate that allows the exhaust flow from both the FFU  150  and the wafer engine  300  to pass out into the ambient environment. Each side of the EFEM is sealed by end plates  156  which mount and seal with the spine  100  (see  FIG. 30 ), the tool interface panel  154 , the panel  152 , and the FFU  150 . As shown in  FIG. 10 , the clean air flow from the FFU  150  and the slide body FFU  420  travel through the mini-environment, or Class-1 area, and out through the bottom panel  152  and the lower channel  106 . The airflow exhausted from the Z slot fan  354  (described hereinafter), which contains particles generated by the vertical drive  380 , also travels through the bottom panel  152 . The airflow from the Z slot fan  354  never enters the clean mini-environment. 
     In general, the spine  100  creates a single reference system to calibrate and align the EFEM components, such as the wafer engine  300  and the FOUP advance assembly  130 . Each separate EFEM component may calibrate to a known and fixed position, such as a vertical strut  102  instead of calibrating and aligning with respect to each other. This method of calibration is greatly simplified over the conventional procedures required today. 
     Spine Structure with a Backbone 
       FIGS. 11–13  illustrate another embodiment of a spine structure. The primary structural elements of this embodiment include a horizontal beam  170 , registration struts  172 , and a front mounting plate  174 . As shown in  FIG. 11 , the horizontal beam  170  is preferably mounted to the bottom portion of each registration strut  172  to form a rigid frame. The front mounting plate  174  is also mounted to each registration strut  172 , providing a surface for the exterior EFEM components (e.g., FOUP advance assembly  130 ) to mount to. The horizontal beam  170  may be manufactured from, by way of example only, an aluminum extrusion, steel tube, a structure made from bent sheet metal, a flat plate, a laminated plate, or most likely a combination of some of the above. The horizontal beam  170  also provides a surface for the linear drive  306  (described hereinafter) to mount to. Similar to the spine structure  100 , this embodiment provides a single reference to mount and align EFEM components. 
       FIG. 12  illustrates that the FOUP door  12  and the port door  140  are preferably still stored in an isolated area within the Class-1 Area. Accordingly, the beam  170  must be spaced apart from the registration struts  172  far enough to allow the FOUP door  12  and the port door  140  to fit between the beam  170  and the registration strut  172 . As shown in  FIG. 12 , separators  171  are placed between each registration strut  172  and the beam  170  to create the storage area. It is within the scope and spirit of the invention to create the storage area through other means. The beam  170  also functions as a protective barrier, preventing particles created by the wafer engine  300  from contaminating the FOUP door  12  or the port door  140 . 
       FIG. 13  illustrates that the support structure or spine may include the beam  170  having a CNC milled aluminum plate  176  mounted to the beam  170  for supporting the x-axis rails  310  and  312 . This structure is further rigidified by a sheet metal U-shaped section  175 . The vertical registration struts  172 , which are mounted to the section  175 , are aligned similarly to the vertical struts  102  in the previous embodiment. As shown in  FIG. 11 , a front mounting plate  172  mounts to the registration struts  174 . EFEM components, such as the FOUP advance assembly  130 , mount to the front mounting plate  172 . 
     The beam  170  may be positioned between the wafer engine  300  and the pod openers below the work space of the wafer handler. The beam  170 , however it is constructed, provides one structural common element that the EFEM components precisely mount to, eliminating the need for time consuming adjustments in the field when an EFEM is installed or replaced. 
     Single Frame/Shell 
       FIGS. 14–16  illustrate yet another embodiment of the spine structure configured as a FOUP docking station. In this embodiment, the spine structure that the EFEM components mount to is a single frame or shell  202 . The frame  202  serves as a single reference for the interior, (e.g., engine wafer  300 ) and exterior components to mount to and align with (e.g., FOUP advance assembly  130 ) components similar to the spine structure  100 . 
     As shown in  FIG. 14 , the spine structure  200  includes three load port assemblies  204  mounted to the frame  202 . Each load port assembly  204  is similar to the load port assembly  130  disclosed in the preferred embodiment. A load port door  206 , which isolates the Class-1 area from outside ambient conditions, corresponds to each load port assembly  204  for engaging and removing the FOUP door from the FOUP shell. It is within the scope and spirit of the invention for the frame  202  to have more of fewer I/O ports. Similarly, the frame  202  may include a filled-in or solid I/O port located between I/O ports where wafers are transferred through. 
     The frame  202  is preferably formed from a single piece of material. By way of example only, the frame  202  may be created by a punch press. The frame  202  may be manufactured from many different materials. By way of example only, the frame  202  may be manufactured from material such as, but not limited to, sheet metal, polypropylene, composites, or plastics. The frame  202  may also include an anodized surface finish to prevent or reduce outgassing. Whether the frame  202  is manufactured from a single piece of material or separate parts, the frame  202  is scalable. Accordingly, the frame  202  may be customized to create as many FOUP I/O ports as necessary for the EFEM. 
       FIG. 15  illustrates several of the EFEM components mounted to the frame  202 . The preferred embodiment of the frame  202 , which is manufactured from a single piece of stainless steel, is flexible. By way of example only, the frame  202  may also be manufactured from an aluminum sheet. The EFEM must be rigid enough to provide accurate support and alignment points for the EFEM components. Additional supports  210  are mounted to the frame  202  to provide rigid and accurate support points for components such as the linear drive  254 , filter unit  220 , FOUP advance assembly  208 , and tool interface plane. 
     To promote air flow through the load port interface, the top surface  201  and the bottom surface  203  of the frame  202  are perforated. A fan/filter unit  220  may be mounted to, and form a seal with, the top surface  201  of the frame  202  to control the rate and quality of the air through the frame  202 . Such fan/filter unit technology is well known in the art and does not require further disclosure. A single fan/filter unit  220  may be appropriate to achieve the air flow rate desired. However, as the frame  202  increases in size and thus volume, the frame  202  may require multiple fans to maintain the desired environmental conditions. If the interior of the EFEM is not isolated from outside atmospheric conditions (not an inert environment), air may be drawn into the clean mini-environment by the FFU  220  and vented out through the perforated holes  212  in the bottom surface  203  of the frame  202 . 
     If the EFEM is an inert system, a flow capture chamber  224  may be mounted to and sealed with the bottom surface  203  of the frame  202  so that the air flow created by the fan/filter unit  220  is completely contained and re-circulated. The end cap  210  may also have a flow return path guiding the air exiting the flow capture plenum  224  back to the fan/filter unit  220  for re-circulation. 
     Due to the minimal enclosed volume created by the frame  202  the present invention is a very efficient system from an air handling standpoint. A mini-environment with a smaller volume of air to control and filter makes it easier to maintain the cleanliness of the air. Inert systems, or systems requiring molecular filters which degrade as more air push through them, also benefit from a mini-environment containing a smaller volume of gas. By way of example only, filters will require changing less frequently if a smaller volume and rate of gas is passed through them. 
     System Volumetric Space Utilization 
     One of the key differentiators of all of the EFEMs previously described (e.g., spine structure, backbone, and frame) is the fundamental change in space utilization. The space utilization feature will only be referenced to the spine structure  100  even though this concept applies to al the embodiments disclosed in this application. In conventional tool front ends, the front end occupies all space from the front of the load port (load face plane) to the process tool face, and from the floor of the fab up to its highest point, typically the top of the FFU and the full width of the front end. 
     An EFEM constructed from the spine structure  100  creates significant space below the load ports  130 , and the clean wafer engine area may be given back to the process/metrology tool or used for other purposes. Additionally, the overall depth of the enclosed area or mini-environment is also decreased from what conventional EFEM configurations require. The front of the wafer engine radial slide body  400  may be rotated into the typically unused area for the FOUP door mechanism resides between the vertical struts  102 . The space may be given back to the process tool as well as the end user who may realize lower foot print requirements for the overall tool. The configuration of the wafer engine  300  takes advantage of these new and smaller space constraints. For example, the radial slide  400  may reach further into the process tool than a non-offset version. 
     As a result of the much smaller envelope of the system it is considerably lighter, and if mounted on the independent rolling frame, may be rolled away from the process tool to provide direct access to the tool. Since the system is also shorter than typical process tools, the space above it may be used for other purposes as well, such as local FOUP  10  buffering for the AMHS system. With conventional overhead hoist AMHS systems, local buffer stations may only be placed between load ports or tools since they require unobstructed overhead path to the load port. With the slide out shelf arrangement, the material could be stored in an otherwise unutilized area directly above the enclosed area of the integrated EFEM. 
     As shown in  FIGS. 30–31 , the system may be integrated with the process tool in several ways. It is designed to require support at four points. Two points in the front at the base of the two outer vertical struts provide attached and leveling points. Two points at the rear lower corner of each end plate provide the rear support locations. The support points could be provided by a roll out frame which would provide an easy way to move the system away from the process tool. It could be supported by frame members from the process tool which could be cantilevered out from the tool or supported from the floor. It might also be a combination of the two where the roll out frame could be used to lift the system off kinematic points provided by the process tool frame. 
     Any of the integrated mini-environments and structures  100  or  200  as previously described mount to the front of a tool associated with a semiconductor process. As used here, such tools include, but are not limited to, process tools for forming integrated circuit patterns on semiconductor wafers, metrology tools for testing various properties and work pieces, and stockers for large scale storage of work piece carriers. As used herein, a tool may be simply an enclosure so that the work piece handling on the back side of the plate as described hereinafter may be carried in an enclosed space. By way of example only, the structure  100  according to the present invention may comprise a sorter for arranging and transferring work pieces with one or more carriers. 
     Alternatively, the structures  100  may comprise a sorter or a stand-alone prealigner. In both the sorter and stand alone prealigner embodiments, the work piece operations are carried out entirely by the EFEM components mounted to the structure  100 . The enclosure that forms the Class-1 Area is also based from the structure  100  provides an enclosed, clean environment in which the work pieces may be handled. In several embodiments of the present invention, the structure  100  may be considered as being part of the tool (see  FIG. 3A ). In other embodiments of the present invention, the system may be affixed to but considered separate from the tool ( FIGS. 29A–29D ). 
     As best shown in  FIG. 10 , the FOUP docking station is formed around the spine  100 . A bottom pan  118  is secured to, and forms a seal with, the bottom support member  106 . In a preferred embodiment, the bottom pan  118  is perforated surface to allow air from the FFU  150  to pass through. The FFU  150  is secured to, and forms a seal with, the upper support member  104 . A wafer transfer plate  122  is secured to, and forms seal with, the bottom pan  118  and the FFU  150 . The wafer transfer plate  122  may include transfer windows  121  that allow the wafer engine  300  to transfer wafers between the Class-1 Area and the process tool. 
     The system forms an air tight seal to maintain the Class-1 environment. An air tight seal is created between both the spine  100  and the bottom pan  118 , the spine  100  with the FFU  150 , and the wafer transfer plate  122  with both the FFU  150  and the bottom pan  118 . Generally, the pressure within the Class-1 Area is maintained at a level higher than that of the atmosphere surrounding the Class-1 Area. This pressure differential prevents unfiltered air from entering the Class-1 Area. Accordingly, airborne particles or contaminates are blown out of the Class-1 Area through the openings in the bottom pan  118 . On occasion tools operate in a hostile environment, such as for example, a pure nitrogen environment. In such an environment it is necessary to completely isolate the Class-1A Area from the outside surrounding environment. A plenum may be secured to, and sealed with, the bottom pan  118 , so that the mini-environment within the structure  100  is completely isolated from atmospheric conditions. A plenum  224  (see  FIG. 14 ) may be mounted to the bottom pan  118  to capture the air and recirculate it back towards the fan/filter unit  150  mounted to the spine  100 . 
     Wafer Engine 
     In general, the wafer engine  300  illustrated in  FIGS. 18–23  minimizes mechanical inertias with respect to frequency of use and criticality of wafer transfer cycle time. By way of example only, some of the benefits resulting from this wafer engine  300  include (1) achieving faster wafer swap times, (2) a lower total system weight, and (3) a more compact, unified package. The wafer engine  300  may operate within any of the embodiments of the unified spine  100  disclosed in this application, or operate as a stand-alone device. 
     A preferred embodiment of the wafer engine  300  is illustrated in  FIGS. 18–19 . The wafer engine  300  includes four main coordinated drives to optimize the transfer of wafers within the EFEM. The four drives move a wafer along an x-axis, a theta axis, a z-axis, and a radial or r axis. 
     The wafer engine  300  has a linear drive assembly  302  that moves the wafer engine  300  along an x-axis. Movement along the x-axis allows the wafer engine  300  to access each FOUP I/O port. The linear drive assembly  302  includes an x-carriage  304  and a rail system  306 . The x-carriage  304  slidably engages the upper x-rail  310  and lower x-rail  312 . The rail system  306  is mounted to the rear mounting plate  116 , and includes an upper x-rail  310  and lower x-rail  312 . The upper x-rail  310  and lower x-rail  312  extend along the x-axis and are substantially parallel to each other. The break lines running through the rail assembly  306  in  FIG. 18  shows that the rail assembly  306  may be of any length. The rail assembly  306  is scalable so that the wafer engine  300  may travel along the rail assembly  306  to access, for example, the wafers stored in each FOUP  10 . The rotational drive  350  of the wafer engine  300  is also mounted to the x-carriage  304 . Thus, movement by the x-carriage  304  drives the wafer engine  300  along the x axis. 
     The wafer engine  300  may also rotate, pivoting about a theta (θ) axis. In a preferred embodiment, and as shown in  FIG. 18 , the rotational drive  350  includes a support column  364  that extends along the theta axis and mounts to a z-axis support  370 . The rotational drive  350  includes a theta motor  362  to drive and rotate the support column  364 . The rotational drive  350  may rotate in either a clockwise or counterclockwise direction. The rotational drive  350  may also mount directly to the vertical drive  380 . Preferably, the theta axis does not travel through the center of the slide body  400 . The advantages of this off-center configuration of the slide body  400  will be discussed later. 
     The rotational drive  350  further includes a fan extension platform  352 . In a preferred embodiment of the wafer engine  300 , and as shown in  FIG. 20 , a z slot fan  354  is mounted to the underside of the fan platform  352 . This configuration of the wafer engine  300  locates the z slot fan  354  near the theta motor  362  and provides and air vent to exhaust the air driven through the z column  380  of the wafer engine  300 . The air flushed through the z column  380  is projected downward, away from any wafer that is being transported by the wafer engine  300  (see  FIG. 21 ). Alternatively, the airflow may be exhausted through, and out the bottom of, the rotational drive  350 . 
     The vertical drive column  380  is mounted to the support member  370  and extends upward along the z-axis. The drive column  380  moves the slide body  400  (described hereinafter) of the wafer engine  300 , and thus the wafer, up and down along the z-axis. In one embodiment, and as shown in  FIG. 19 , the drive column  380  is an elongated column that extends substantially perpendicular from the support member  370 . A drive assembly is located within the drive column  380  and includes a z-drive motor  382 , a z cable way  384 , a z guide rail  386 , and a z ball screw  388 . Such drive means are well known in the art and do not require further disclosure. It is within the scope and spirit of the invention to move the slide body mechanism  400  by other means. 
     The slide body  400  preferably includes an upper end effector  402  and a lower end effector  404  for quickly swapping individual wafers along the r-axis. The slide body  400  supports the upper and lower end effectors  402  and  404  such that they are parallel to the wafers stored in each FOUP  10 . As shown in  FIG. 19 , the upper end effector  402  and lower end effector  404  travel along a similar rectilinear path. The upper end effector  402  and lower end effector  404  are separated by a distance sufficient to allow the lower end effector  404  and the upper end effector  402  to simultaneously store wafers. The slide body  400  includes radial drive motors  410  for moving the upper end effector  402  and lower end effector  404  linearly along the radial or r-axis. 
     The upper end effector  402  is supported by an first support  406  and the lower end effector  404  is supported by a second support  408 . The upper end effector support  406  and lower end effector support  408  each slidably engage and travel within a radial guide rail  410  that extends substantially across the length of the slide body  400 . Each radial drive motor  410  drives a radial drive belt  414 . The radial drive belt  414   a  is connected to the first support  406 , and the second radial drive belt  414   b  is connected to the second support  408 . The radial drive motor  410  may rotate in a clockwise or counter-clockwise direction to rotate the radial drive belt around a radial drive pulley  416  and an end idler pulley  418  and to extend and retract the respective end effector. Such a drive mechanism is well known in the art and does not require further disclosure. It is within the scope and spirit of the present invention to have other means to move a wafer along the radial or r-axis. 
     The wafer engine  300  has many moving parts. Moving parts tend to create particles. For example, the continual extension and retraction of the upper end effector  402  and lower end effector  404  will create particulates within the mini-environment. To prevent the particulates from contaminating the wafer located on either end effector, a slide body fan/filter unit (FFU)  420  is mounted to the underside of the slide body  400 . The slide body FFU  420  continuously pulls air in through the slide body slide slots  420 , pulls the air through the slide body  400 , filters the air, and then exhausts the air out into the Class-1 Area. This localized filtering of the air flow greatly reduces the amount of particles placed into the Class-1 Area. 
     Conventionally, most mini-environments include a single fan/filter unit that circulates the air through the mini-environment and only filters the air flow as it flows into the EFEM. Any particulates created within the mini-environment downstream of the fan/filter unit remain in the clean area until they are exhausted out of the EFEM. It is desirable to minimize the number of particulates within the mini-environment especially since the trend in semiconductor manufacturing more and more requires a lower tolerance of particle contamination on the wafers. 
     The localized filtering of the wafer engine  300  removes particles created by any rotating or sliding mechanism located on the wafer engine  300  as the particle is created. In a preferred embodiment, and as shown in  FIGS. 19 and 21 , a local fan/filter unit or fan system is located approximate to both linear drives of the z column  380  and slide body mechanism  400 . As specifically shown in  FIG. 21 , the fan/filter unit mounted to the slide body mechanism  400  exhausts filtered air into the clean mini-environment, while the z slot fan system of the vertical drive  380  exhausts unfiltered air through the bottom plate of the EFEM. The wafer engine  300  filters and exhausts air into the Class-1 Area of the EFEM. If the wafer engine  300  did not have the fan/filter mounted to the slide body mechanism  400 , particles created by the slide body mechanism  400  would travel through the Class-1 Area and contaminate the wafer supported by either end effector. 
       FIG. 20  illustrates another embodiment of the wafer engine  300 . In this embodiment, the slide body  400  engages the z column  380  such that the z column  380  is substantially along the r axis. Similar to previous embodiments of the wafer engine  300 , this embodiment includes a theta motor  362 , a vertical drive column  380  and a radial slide body  400 . The theta motor rotates the wafer engine about the theta axis, the z column moves the radial slide body  400  linearly along the z axis, and the radial slide body  400  moves the end effector  401  along the radial or r-axis. Accordingly, the wafer engine and thus the wafer will rotate about the theta axis any time the theta motor  362  rotates. This embodiment may also include a fan/filter unit mounted to the radial slide body  400  in a v slot fan similar to the previous embodiment of the wafer engine  300 . 
     As previously mentioned, the slide body  400  of the wafer engine  300  may include different configurations of end effectors. As illustrated in  FIGS. 18–19 , the upper and lower end effector  402  and  404  may include a passive edge support. Such a configuration is known in the industry as passive edge grip end effectors for 300 mm wafers.  FIG. 22  illustrates that the upper end effector  402  may include an active edge grip, while the lower end effector  404  may include a passive edge support. Alternatively, the end effectors  402  and  404  may include any combination of, for example, a vacuum grip with backside contact, a reduced contact area, removable pads. 
     Similarly, the radial drive  400  may include different types of end effector for handling wafers at different stages. For example, one end effector may handle only “dirty” wafers, while the second end effector may handle only “clean” wafers. Alternatively, one end effector may be designated to align and read the wafer ID before transferred to the process tool, while the second end effector may include high temperature pads for handling hot wafers after being processed. 
     Integrated Tools in Wafer Engine 
     A conventional wafer handling robot transports individual wafers, for example, from a FOUP  10  to a separate processing station. The processing station inspects or aligns the wafer and then the wafer handling robot may transport the wafer to the next station. Often the wafer handling robot must sit idle or return to a FOUP  10  to transport a second wafer while the process station operates. Such an operation reduces the throughput of the system. 
     In one embodiment, the wafer engine  300  includes a slide body  400  that may perform one or several of these functions normally performed at a separate processing station. Integrating one or several of these functions into the slide body  400  will increase the throughput of the system and reduce the footprint of the EFEM. 
       FIGS. 22–23  illustrate a wafer engine  300  equipped with a wheeled aligner  440  and ID reader  430  mounted on the slide body  400 . This embodiment is similar to the wafer engine  300  as shown in  FIGS. 18–19 , with the addition of a wheeled aligner  440  mounted on the upper end effector  402 , and an ID reader  430  mounted to the slide body  400 . It is within the spirit and scope of the invention for the lower end effector  404  to include a wheeled aligner. 
     The ID reader  430  may view up or down for reading marks on top and/or the bottom surfaces of the top or bottom of the wafer. It is within the scope and spirit of the invention for the ID reader  430  to be mounted to the vertical drive  380 , or be mounted in a fixed location elsewhere on the wafer engine  300 . IN the preferred embodiment, it is advantageous to mount a top side ID reader  430  on the slide body  400  for fast ID reading. A second ID reader may be mounted at a fixed location elsewhere in the EFEM for reading the bottom side T7 mark for confirmation or clarification of wafer ID if required. 
     If ID reading is required but wafer orientation is not important, the aligner may be eliminated and the ID reader  430  may view the ID mark in whatever location the wafer arrives on the end effector. To facilitate this operation, the ID reader  430 , or a mirror assembly, may be rotated above the surface of the awfer to view the ID mark. This eliminates the need to rotate the wafer for ID reading and thus improves cleanliness and throughput. 
     An aligner controls the rotation of the wafer about an axis,, such as by wheel or other means.  FIGS. 23–24  illustrate one embodiment of an end effector with a wheeled aligner  440 . The wheeled aligner  440  includes a drive system  449  and a paddle plate  442 . The paddle plate  442  is the main support for the wafer. Located at the end of the paddle plate  442  are two sets of passive tip wheels  446  and two pads  448 . The wheels  446  and pads  448  support the wafer at different times during alignment. A drive wheel  450 , located at the back end of the paddle plate  442 , supports the wafer along a third contact surface while the wafer is being aligned. 
     In one embodiment, wheeled end effector  440  slides underneath a wafer located in a FOUP  10  and is raised until the wafer is supported by the pads  448 . The pads  448  preferably only support the wafer along its bottom edge. To align the wafer, the wafer is pushed forward by the drive wheel  450  and up onto the wheels  446 . The wafer is lifted off the pads  448  and is fully supported by the drive wheel  450  and the tip wheels  446 . At this point the drive wheel  450  may rotate to spin the wafer in situ. This operation may be performed while the wafer engine  300  is transporting the wafer. The wafer engine  300  does not have to remain in place to align the wafer. 
     Alternatively, as shown in  FIG. 26B , the slide body  400  may include a vacuum chuck aligner  411 . The drive mechanism for the vacuum chuck aligner  411 , including a lift and rotation axis, may reside inside the slide body  400 . A sensor  409  may be mounted to the end effector  403  to locates the edge of the wafer while it remains on the end effector. The sensor  409  may also be mounted to an structure that is independent of the end effector  403 . In general, the sensor  409  may be located at various locations as long as the sensor  409  can be positioned to read the top surface of the wafer. 
     The edge position may be mapped relative to the rotation angle to find the center and orientation of the wafer. The sensor  409  functions as a secondary feedback device. The location of the sensor  409  is known relative to the wafer at all times. Thus, the sensor  409  may send error signals indicating that the wafer is not aligned. Since the aligner receives additional error data from the sensor  409 , an aligner with such a sensor will improve the accuracy of the aligner. The wafer can then be reoriented by the chuck  411  and placed on center at the next drop off station by the wafer engine  300 . 
     The sensor  409  may be mounted independently within the EFEM and be a separate component from the wafer engine  300 . In such a configuration, the wafer is placed on the chuck  411  that can rotate. The sensor  409 , mounted on a mechanism that has position control and measuring means (not shown), is moved to the proximity of the wafer edge until the sensor signal is at a desired level. The wafer can then be rotated while the sensor mechanism uses the signal from the sensor  409  to keep the position of the sensor  409  at the this desired level, effectively keeping the sensor  409  at the same relative position to the wafer edge. As the wafer is rotated, the sensor position is recorded with respect to the angular position of the wafer. This data represents the change in radial position of the wafer edge with respect to wafer rotational position, and can be used to calculate the center of the wafer with respect to the center of the wafer chuck and the orientation of the fiducial. If the sensor signal magnitude is also recorded along with the sensor mechanism position, it can provide additional edge position information that could improve the accuracy of the wafer center calculations or fiducial orientation. 
     The wheeled end effector aligner  440  may include other components such as, but not limited to, an optical notch sensor  452  to detect the notch along the edge of the wafer. For example, once the notch has been located along the edge of the wafer by the optical notch sensor  452  the drive wheel  450  may rotate the wafer to the desired position and retract back, allowing the wafer to fall back down onto the pads  448 . This operation may be performed while the end effector is in place or is moving. The ability to align the wafer while it is being transferred between FOUPs  10 , or between a FOUP  10  and a processing tool, greatly reduces or eliminates the amount of time that an end effector must sit idle. Further, there is no need for a separate processing station if the wafer engine  300  can align a wafer “on-the-fly.” 
     The slide body  400  enables a stable mounting platform for a variety of auxiliary functions, measurements, and sensors to acquire various wafer data. By way of example only, components may be integrated into or mounted to the slide body  400  to detect a wafer edge, detect the notch location on the wafer, read the OCR/bar code, perform particulate counting (back side or front side), determine film thickness/uniformity or circuit element line width, and detect resistivity (via contact probes or non-contact means) and wafer thickness. Other processes known in the art for inspecting and marking a wafer may be incorporated into the slide body  400 . 
     In order to transfer workpieces from a carrier, the end effectors  402  and  404  move horizontally under the workpiece to be transferred and then moved upward to lift the workpiece off its resting place. The end effectors  402  and  404  may also include edge grips for supporting the workpiece at its edges. Alternatively, the end effectors  402  and  404  may be a blade type end effector for supporting a workpiece by its bottom surface. In such embodiments, a vacuum source (not shown) may be affixed to or remote from the paddle plate  442 , which creates a negative pressure that is communicated through the workpiece handling robot via flexible vacuum tubes to the surface of the end effector blade. Upon activation of the vacuum source a negative pressure is formed at the surface of the end effector blade, creating a suction capable of holding a workpiece firmly thereon. A vacuum sensor (not shown) of known construction may also be provided on the robot and associated with the vacuum system for detecting when a workpiece is engaged with the end effector and restricting the pull of air through the vacuum tubes. It is understood that the present invention is not limited to the end effector described above and that a variety of end effector designs may be used as long as the end effector has the capability to pick up and drop off workpieces. 
     The slide body  400  may also be adapted to process a wafer and environmentally isolate the wafer from the Class-1 Area. By way of example only, the slide body  400  may include process tools to either heat or cool the surface of the wafer, or conduct thermal surface processing. In another embodiment, the slide body  400  may include a housing (not shown) that a wafer may be retracted into and temporarily stored within while the wafer engine  300  is transferring the wafer out of the process tool and within the Class-1 Area. The housing provides an inert or clean environment that has a better than Class-1 Area environment. Such a system may include floating oxygen or an inert gas over the surface of the wafer while it is being transported. 
     Dual Swap Capability 
     The time between when a processed wafer is removed from the process station and when a new wafer is placed into the process station is known as the “swap time.” For most process tools, the throughput is determined by the process time plus the swap time. Reducing either increases throughput. The process time is the purview of the tool manufacturer, the swap time is the purview of the capital EFEM manufacturer. 
     For a conventional single end effector wafer handling robot in an EFEM (see  FIG. 17 ), the swap time may be 8 to 16 seconds, depending on the station arrangement and the speed of the wafer handling robot. The following sequence of operations are commonly used by such a robot to swap a wafer at a process station. The items contributing to the swap time are in italics. Items outside of the critical path determining throughput are in (parenthesis). 
     1. Get wafer from process station 
     2. Put processed wafer to load port 
     3. Get aligned wafer from aligner 
     4. Put aligner wafer to process station 
     [Begin Processing Wafer] 
     5. (While processing, robot get new wafer from load port) 
     6. (While processing, robot put new wafer to aligner) 
     7. (While processing, aligner align wafer) 
     [Repeat] 
     A rapid swap robot (e.g. wafer engine  300 ) has two end effectors and therefore can dramatically reduce swap time by performing the same function as above using the following abbreviated sequence: 
     [Process Complete] 
     1. Get wafer from process station with paddle  1   
     2. Put aligned wafer to process station with paddle  2   
     [Process Wafer] 
     3. (While processing, get new wafer from load port) 
     4. (While processing, put new wafer to aligner) 
     5. (While processing, aligner align wafer) 
     6. (While processing, get aligned wafer from aligner) 
     [Repeat] 
     In this case, the swap time may be reduced by 3 to 6 seconds depending on the speed of the robot. The overall time for the robot to complete all of its motions may be slightly reduced as well. The overall motion time is of primary importance in applications where the process time is very low and therefore the items in parenthesis above would enter into the critical path or throughput. 
     A further improvement on throughput and reduction in total robot motions can be made if the robot has align-on-the-fly capability as well as rapid swap capability like the wafer engine  300  having a wheeled end effector aligner  440 . Align-on-the-fly does not reduce swap time, but it does reduce overall robot motion time and therefore increases throughput where the process time is low, or where the robot must support multiple process stations. Also, by reducing the number of robot motions and wafer handoffs, align-on-the-fly can increase robot life and improve cleanliness. 
     For the align-on-the-fly rapid swap wafer engine, the comparable sequence of operations is: 
     [Process Complete] 
     1. Get wafer from process station with paddle  1   
     2. Put aligned wafer to process station with paddle  2   
     [Process Wafer] 
     3. (While processing, get new wafer from load port) 
     4. (While processing, align wafer and simultaneously move to position for next rapid swap) 
     [Repeat] 
     Unlimited Z-axis Motion 
       FIG. 25  illustrates a wafer engine  300 ′ including an off-center slide body  400  having a wheeled aligner  454  and ID reader  430 , and an extended z-axis drive column  380 ′. This embodiment of the wafer engine includes an extended z column  380 ′ to, for example, to access a stocker, or a load port or process station that may be located above the FOUP I/O port. Basically, the height of the z-axis drive column  380  or  380 ′ is unlimited. The wafer engine  300  or  300 ′ may access a wafer located within a FOUP  10  by moving the upper end effector  402  or the lower end effector  404  along the radial or r-axis. The distance that the upper end effector  402  or lower end effector  404  must travel into the FOUP  10  is designed to be a short distance since this is the most often required motion of the wafer engine  300  or  300 ′. The height of the vertical drive column  380  or  380 ′ does not effect the distance that either the upper end effector  402  or lower end effector  404  must travel. Thus, the height of the vertical drive column  380  or  380 ′ does not effect the motion along the radial or r-axis. 
     Conventional wafer handling robots must move the z drive column linearly towards the FOUP  10  so that the end effector may access and remove the wafer from the FOUP  10 . Accordingly, a tall vertical drive column for such a wafer handling robot requires moving a large vertical column by a motor or a belt drive. Moving such inertia places great strain on the wafer handling robot. The wafer engines disclosed in this application are an improvement over such wafer handling robots because the axis of motion, along the radial or r-axis, which is the most commonly traveled are also the shortest distances. 
       FIG. 27A  illustrates that a conventional linear slide robot may reach into the processing tool 250 mm for transferring and retrieving wafers into the process tool. Similarly, a convention wafer handling robot requires a minimum clearance within the EFEM work space of 520 mm so that the wafer handling robot can maneuver within the EFEM.  FIG. 27B  illustrates the reach and swing clearance advantage of the off-center slide body rotation about the theta axis. In a preferred embodiment, the off-center slide body axis of rotation, shown as the theta axis in  FIG. 19 , is offset by approximately 50 mm. The off-center axis of rotation for the wafer engine  300  has two distinct advantages. First, the maximum reach of an end effector (e.g., upper end effector  402  or lower end effector  404 ) into the processing tool is increased to 350 mm. Second, the minimum clearance required within the EFEM work space is reduced to 420 mm. The maximum reach and minimum clearance distances are by way of example only. Increasing the reach of the end effector into the process tool, while decreasing the minimum clearance required for the wafer engine  300  to maneuver within the EFEM reduces the overall footprint of the EFEM. 
       FIG. 28  illustrates an example motion sequence of the wafer engine  300  having a rapid swap slide body  400  with off-center rotation axis. By way of example only,  FIG. 28-1  illustrates the wafer engine  300  lifting the wafer at load port area one.  FIG. 28-2  illustrates the wafer engine  300  retracting the wafer from within load port one along a radial axis.  FIG. 28-3  illustrates the wafer engine  300  rotating about the theta axis and simultaneously moving back along the x-axis to avoid collision with load port one.  FIG. 28-4  illustrates the wafer engine  300  moving along the x-axis towards the I/O port of the processing station.  FIG. 28-5  illustrates the wafer engine  300  continuing to rotate about the theta axis and along the x-axis to position the wafer for entry into the processing station.  FIG. 28-6  illustrates the wafer engine  300  waiting for the process to complete.  FIG. 28-7  illustrates the wafer engine  300  swapping the processed wafer for the new wafer ready to enter the processing station. Finally,  FIG. 28-8  illustrates the wafer engine  300  retracting the processed wafer in a radial axis while simultaneously moving along the x and theta axis to return the processed wafer into load port one, two or three. 
     The wafer engine  300  and  300 ′ described above provides several benefits over conventional wafer handling robots. For most wafer handling applications, radial motion needed to insert and remove wafers into and out of a FOUP  10  or a process station has the highest duty cycle and longest overall distance traveled. The wafer engine  300  places the radial drive  400  as close to the wafer as possible before attempting to access the wafer. This placement reduces the moving mass and motion time of the upper end effector  402  and lower end effector  404 , and wear. 
     The z-drive column  380  occupies the same volume of space that is swept out by the wafer as the wafer engine  300  rotates. The drive column  380  also does not extend below the work plane. A conventional wafer handling robot must utilize the area located below the wafer plane to access some of the wafers within the FOUP  10 . Typically, the end effector is mounted to the top of a column that travels up and down along the z axis. The column takes up space that could otherwise be used for other purposes. Similarly, when the column moves horizontally along the x axis, the area located below the wafer plane must substantially empty so that the column does not run into and damage any obstacles. 
     There are several variations and/or modifications that can be made to the wafer engine  300  that still have the unique elements and benefits previously listed above. By way of example only, the x-axis drive  302  may be eliminated for some applications. Similarly, a single radial axis may suffice. Further, for some applications (e.g., sorters) may not require a rotational drive. Instead, the z-axis drive  380  would mount to the x-carriage  308 . A sorter application, for example, may have all of the load ports mounted facing the same direction, and if the alignment and ID reading is integrated into the wafer engine  300 , the need to rotate would be eliminated. 
       FIGS. 29–31  illustrate several configurations of the integrated system.  FIG. 29A  illustrates the integrated system mounted on a roll out frame  199 . As previously mentioned, conventional EFEMs extend all the way down to the floor of the wafer fab. With the space savings derived from constructing an EFEM from a spine structure  100  or other embodiments disclosed in this application, the footprint of the integrated system is greatly reduced. As shown in  FIG. 29A , the integrated system is mounted on a roll out frame  199  so that the load port assemblies remain at the SEMI standard height of 900 mm. When this integrated system is bolted to the front end of a processing tool, and in a preferred embodiment, there will be approximately 2 feet of open space located beneath the integrated system and the wafer fab floor. This space has never been available in a wafer fab before. Such a space will allow semiconductor manufactures to place other items such as an electrical control box underneath the integrated system. 
     Alternatively, a processing tool may now have a maintenance access that can be reached by crawling underneath the integrated system. The roll out frame also improves the overall maintenance features of the processing tool that the integrated system is bolted to. By way of example only, if maintenance needs to be performed on the processing tool, the integrated system may be unbolted from the processing tool, the wheels of the roll out frame may be unlocked, and the integrated system may be rolled away from the front end of the processing tool. A conventional EFEM that is bolted to the processing tool does not contain wheels that the EFEM can be rolled out on, and is typically such a heavy device that it requires more than one maintenance person to lift the EFEM away from the process tool. As previously mentioned, the integrated system of the present invention weighs only several hundred pounds and thus can be easily rolled away from the front of the processing tool by a single maintenance person. 
       FIGS. 30A–B  illustrate the integrated system integrated into a process tool. By way of example only, the system of the present invention may be integrally formed and mounted to a process tool. One advantage of this system is that if every process tool within the wafer fab had an integrated system mounted to it, the wafer fab would have a front and load system that can be configured to the needs of each process tool yet contain a similar environment to reduce the need for stocking spare parts and training maintenance personnel. 
     Electrical Control System 
     Conventional EFEMs must contain a power distribution that is compatible with the power requirements for countries across the world. Therefore, most EFEMs today must be able to adapt to either a 110V or a 220V system. Being able to a adapt to either power system requires that an EFEM include power components such as step down or step up transformers as well as other electrical components. Such electrical components must be mounted within the EFEM and thus increase the footprint of the EFEM. 
     The EFEM of the present invention is designed for all electrical components such as the FOUP advance plate assembly, the wafer engine  300  and the fan/filter unit  150  to operate all under a 48V system. In general, the EFEM of the present invention may be electrically connected to either a 110V or 220V system that will stepped-down to 48V to control all of the elements described previously. Simplifying the electrical distribution system of the EFEM eliminates the need for many of the conventional power distribution components such as the step up transformer and thus further decreases the footprint of the EFEM of the present invention.