Abstract:
A storage/buffering system for the stocking and/or buffering of substrate and/or substrate carriers in a process environment includes a 6-axis robot. An end-effector is connected with the robot providing an additional one degree of freedom and a mechanism for grabbing and moving of substrate and/or substrate carriers. The robot is mounted in an inverted orientation to a removable service cart for easy removal of the robot to a service area in the event of breakdown. The robot receives commands from a programmable controller connected to control the robot and configured to direct the arm of the robot through a set of movements. Product is loaded in and out of the system through I/O load ports. Product is stored inside the storage/buffering system on a plurality of storage locations, each with product presence/absence detect sensor.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application No. 60/397,389 filed Jul. 17, 2002 entitled: Robotic Storage Buffer System for Substrate Carrier Pods; and United States provisional patent application No. 60/310,558 filed Aug. 6, 2001 entitled: Robotic Storage Buffer System for Substrate Carrier Pods or the Like. 
    
    
     TECHNICAL FIELD 
     The present invention relates to devices and methods for the stocking/buffering of substrate and substrate carriers and particularly to stocking/buffering using a robot arm. 
     BACKGROUND OF THE INVENTION 
     A semiconductor fabrication line performs various processing steps to wafer substrates to produce integrated circuits. Present fab systems use reticle or full wafer masks which are stored in standard mechanical interface (SMIF) pods, front opening unified pods (FOUPs), or stocked as bare masks. Wafer sizes vary depending on the semiconductor process; typical maximum sizes are 200 mm and 300 mm in diameter. Wafers can be stored in SMIF pods or FOUPs, which hold as many as 25 substrates. 
     Intermediate term stocking and short term buffering of substrate carriers is needed to supply the articles to the manufacturing steps as needed. To address the high throughput demands of many manufacturing environments a stocking/buffering system is needed to store carriers in quantity and transfer it via an automated method. The system is either placed in a stand-alone mode where its purpose is to feed material to the Fab itself or in a local mode where it feeds a local tool or tool cluster. 
     Presently, the main design technique in building these systems automation components is the use of Cartesian slide systems configured in such a way as to achieve the desired motion profile through a plurality of degrees of freedom, usually 3 or 4. The automation components are a combination of linear positioning stages and other motion systems. 
     One of the major problems of this method has been the automation component itself. Usually being an aggregation of several linear slides, the reliability and serviceability of such systems have been consistently poor. Linear slide systems are subject to alignment problems, which can cause binding and malfunction resulting in a low mean-time-between-failure performance. Also since this is not a true unified automated solution, the design, assembly, and programming time is greatly increased. 
     Another method of automation utilized is a selective or single compliant assembly robot arm (SCARA) robot mounted on an extra vertical axis of motion to achieve a specific Z height. Although this method is much more reliable than the Cartesian system, the SCARA robot needs a very large footprint to negotiate the product through. This in many cases, results in a system that is unacceptable in size to end users where applications are space critical. 
     The prior art stocking systems do not have the capability of selecting a carrier from a stocking area and transferring it directly to front end automation with multiple load ports. 
     A need exists for a method and apparatus for stocking substrate carriers that is small in footprint, highly reliable, and easy to service. 
     SUMMARY OF THE INVENTION 
     A new robotic storage system utilizes an invert mounted 6-axis articulated robot arm to transport objects such as FOUPs or SMIF pods between a storage location and an I/O load port. A seventh degree of freedom is provided by an end-effector to accomplish motion within a small space. FOUPs and SMIF pods are stored in a high density arrangement on shelves within a storage area. Each storage location within the storage area has a presence/absence detection sensor. 
     The present system provides in a storage buffer system the ability to stock and randomly access a large number of substrate carrier pods, or other containers, fixtures, parts, or assemblies used in an automated production process. The system uses a minimal footprint while providing a simple and reliable design that has a low repair time. 
     Suspending an invert mounted robot from the top of the enclosure provides clearance for the robot to function without obstruction. Floor area is therefore available for other system components and additional area for stored items. A FOUP or SMIF pod cleaner is one example of a process that can be incorporated into the system using this area. Additionally, this configuration provides improved access to the robot for maintenance or replacement. 
     The seventh axis on the robot, using a swiveling end-effector, allows the robot to capture material at all locations effectively, thus making accessible locations that would otherwise be inaccessible without the additional axis. 
     The seventh axis can be implemented with a passive or active control. A passive system uses an upper dowel and bearing to permit the pod holder to swing freely, relying on gravity to maintain an upright orientation. An active system uses electrical, pneumatic, or hydraulic mechanisms to maintain the end-effector in the desired orientation. 
     An automatic teaching capability uses proximity sensors, angle encoders on the robot axes, and torque feedback from the robot motors to allow the robot system to sense locations and obstructions and thereby define the location of features in the storage system and the optimum trajectory for movement between points. 
     The storage system is suitable for intermediate term stocking and short term buffering of articles. The stored articles can be substrate carriers, for example front opening unified pods (FOUPs), standard mechanical interface (SMIF) pods, or substrates without carriers. 
     A removable service cart provides access to the interior regions of the system to expedite servicing the system and it subassemblies. 
     The device comprises a robot including an arm movable in a plurality of degrees of freedom, the arm having a free end. An end effector is connected the robot and has a clasping end mounted to the arm proximal to the free end so as to be positionable by the robot. The robot positions the clasping end of the end effector with respect to the substrate or substrate carrier as to properly position the end effector for pick up of object. The end effector has one degree of freedom to allow greater flexibility for the robot to access storage locations. The robot is mounted inverted to facilitate greater mobility in a small confine without the robot structure interfering with access of storage locations. 
     The present invention uses a method of stocking/buffering substrate and substrate carriers comprising the following steps: 
     providing a robot having an arm movable in a plurality of degrees of freedom and an end effector connected with the robot; 
     automatically moving the arm to align the end effector to pick up or place material in and out of buffer system. 
     A buffer system constructed and operated in accordance with the present invention enables a system that is completely automatic in operation, has a minimized footprint, operates reliably, and has a rapid repair time. 
     The buffer system is capable of handling the FOUP or SMIF pods and transferring directly to the process equipment for loading and unloading. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the robotic stocking/buffering system in accordance with the present invention; 
     FIG. 2 is an exploded view of the robotic stocking/buffer system with the robot cart assembly detached from the main system. 
     FIG. 3 is a detailed isometric view of the system with covers and doors removed; 
     FIG. 4 is an isometric view of the removable robot cart assembly. 
     FIG. 5 is a side and front view of the removable robot cart assembly. 
     FIG. 6 is a detailed view of a shelf suitable for storing substrate carriers inside the robotic stocking/buffer system. 
     FIG. 7 is an enlarged isometric view of the end effector detailing product capture and oscillation dampening features. 
     FIGS. 8-12 show a series of images demonstrating a capture sequence to a substrate carrier for a passive end effector version. 
     FIGS. 13-15 is a series of images demonstrating the pivot axis on the end effector, showing the end-effector attachment arm in the horizontal, 90 degree and 180 degree position respectively. 
     FIG. 16 shows the present invention robotic stocking system interface to a front end automation and process tool. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an embodiment of a robotic stocking/buffering  10  for the stocking and/or buffering of substrates and/or substrate carriers  11 . FIG. 2 is an exploded view of the robotic stocking/buffer system with the removable service cart assembly  15  detached from the storage enclosure  40 . Robot  12  is used for transporting stored items within the storage system  10 . Robot controller  16  is shown, which commands the operation of robot  12 . Sliding doors  42  function as a safety shield to prevent operator injury when robot  12  accesses objects in I/O port  17 . Door  43  provides access for servicing. 
     Referring to FIG. 3, an interior view of storage enclosure  40  with removable cart  15  engaged, substrate carriers  11  are positioned in storage locations  18 . Substrate carriers  11  rest on shelves  35 , which are adapted to hold specific items. Kinematic couplings  34  define the installed position of removable service robot cart  15  allowing repeatability in position when removal and replacement occur. Bolts secure the service cart  15  to the storage enclosure  40 . Pneumatic actuators  36  cause sliding doors  42  to slide open to place objects in I/O load ports  17 . Sliding doors  42  slide to a closed position before robot  12  attaches to the object. Magnetic sensors indicate the limits of travel of pneumatic actuator  36  and sliding doors  42 . 
     Referring to FIG. 4, the removable service cart  15  is a structure that is a separable from the storage enclosure. Robot  12  is mounted to a section of the cart frame. The removable service cart  15  is supported on a plurality of casters  33  so that the cart can be rolled to a service bay in the event of failure. In the event of removal and reinstallation, accurate alignment is critical to avoid re-teaching the robot point locations. Therefore, a plurality of kinematic couplings  34  located at the top and bottom of the cart frame that mate with couplings in the storage enclosure are used for accurate relocation. 
     FIG. 5 show side views of removable service cart  15 . 
     Storage enclosure  40  and removable service cart  15  are constructed from welded stainless steel tubing. 
     FIG. 6 shows a detailed view of a shelf suitable for holding FOUPS. Kinematic pins  39  hold the FOUP in a predetermined position. Sensors  38  indicate the presence or absence of an item on the shelf. The sensors can be reflective, micro switch, Hall Effect, or any other sensor that responds to the presence of an item. The sensor signal is an input to control software that directs robot movement and maintains an inventory of stored carriers and available storage locations. The sensors also provide confirmation of a placement or removal operation of a carrier from a storage location by the robot. FIG. 6 shows a dual FOUP Shelf; other shelves can be adapted to hold varying numbers of FOUPs or other stored objects. 
     A shown in FIG. 8, a robot  12  has a multi-segment arm  13  movable within a plurality of degrees of freedom. An attachment arm  23  connects to an end effector  14  and is positionable by the robot to grasp objects. 
     The robot  12  is preferably an articulated arm robot, for example commercially available from Samsung Electronics, Kawasaki Robots, or Fanuc Robotics. Fanuc Robotics model M-6iB is a suitable robot. The robot  10  has an arm  13  that is movable within six degrees of freedom (DOF). The robot  12  includes a base  22  configured to rotate within a horizontal plane (first DOF). The robotic arm  13  further includes an upper arm  26  having an upper end  26   a  pivotably attached (second DOF) to the shoulder  24  by means of a laterally extending shaft and servo motor  25 . The arm  13  also includes a “forearm”  28  having a first end  28   a  pivotably attached (third DOF) to the free end  26   b  of the upper arm  26  by means of a pivot shaft  27 . The forearm  28  is pivoted about shaft  27  by movement of actuator arm  29  pivotably connected at end  29   a  to forearm  28  and at end  29   b  to shoulder  24 . Further, a “wrist”  30  of the arm  13  is attached to the free end  28   b  of the forearm  28  and is capable of moving in the following three manners: by pivoting about the free end  28   b  of the forearm  28  (fourth DOF), by “spinning” about an axis  31  extending along the centerline of the forearm  28  (fifth DOF), and by spinning about the axis  31  (sixth DOF). 
     A robotic system is described in Soska, U.S. Pat. No. 6,369,353 entitled “Robotic laser tire mold cleaning system and method of use, incorporated herein by reference”. This reference discloses details of the operation of robot motion. 
     Robotic arm  13  includes an end effector  14  mounted to the wrist  30 . An end effector is the working tool that is positionable by movement of the robotic arm  13  within one or more of the degrees of freedom. 
     The forgoing describes one approach to constructing and operating a robot. The robot can be constructed in other ways known within the field of robotics to achieve the movement needed for moving objects in the buffer system. 
     As shown in FIG. 7 a standard pneumatic gripper  21  is mounted above the clasping end  19  around the pivot axis shaft  20  and when actuated, closes on shaft increasing friction, thereby dampening oscillation of the pivot axis  20 . 
     The robot  12  includes a plurality of electric servomotors actuating and controlling the movement of the base  22  and the various portions of the arm  13  described above. However, any other appropriate means for actuating the movements of the components of the robot  12 , such as for example, hydraulic or pneumatic motors can be utilized. 
     The robot  12  can be constructed in any other manner that enables the robotic storage/buffering system  10  to function as described in detail below. For example, the robot  12  can alternatively have a wrist  30  that is configured to spin, to rotate within a vertical plane, and to rotate in horizontal plane as opposed to spinning along axis  31 . Further, the robot  12  may optionally include a machine vision system provided by, for example, video cameras connected to a video processor, so that the robot  12  can recognize the location of the end effector and adjust its position to ensure that the storage/buffering system  10  performs as desired during a load or unload operation, as described below. 
     FIGS. 8 through 12 show robot  12  in various stages of movement to capture a FOUP. FOUP  11  shown is representative of any object the robot captures. 
     Referring to FIG. 13, the end effector  14  includes a clasping end  19 , an attachment arm  23 , a pivot axis  20 , and a pneumatic gripper  21 . The clasping end  19  is the mechanism whereby product is captured for transfer. The clasping end can be either a passive or active grip system depending on the substrate and/or substrate carriers  11  used. In this case a passive system is implemented to secure 300 mm Front Opening Unified Pods (FOUPs) that are used in transferring wafers during semiconductor processing. In FIGS. 13-15, the pivot axis  20  allows further range of motion when mounted on robot. 
     Controller  16  is used for controlling the operation of the robot  12  and end effector  14 . During a load or unload operation, the controller  16  directs the robotic arm  13  so that the end effector  14  is moved through at least one predetermined set of movements with respect to substrate and/or substrate carrier  11 . The predetermined set of movements causes the end effector  14  to actively or passively clasp the substrate or substrate carrier  11 . The controller  16  also controls the activation and deactivation of the end effector  14  if an active one is used so that the end effector  14  clasping mechanism  19  is turned on and off at appropriate times during the load or unload operation. Further, the controller  16  is fully programmable so as to be capable of actuating the robotic arm  13  to move through a plurality of different predetermined sets of movements. Such controller programmability allows the storage/buffering system  10  to be used with various substrates  11  having different sizes and/or shapes. The controller  16  is preferably the standard control system provided with the commercially available robot  12 , although the controller  16  can alternatively be a separately provided personal computer, a programmable logic controller (“PLC”) or any other suitable programmable device connected with the robot  12  and with the end effecter  14 . 
     When in operation, product is transferred in and out of the system via a plurality of I/O load ports  17  where product is presented to and from the environment external to the robot. The I/O load ports  17  can be either standard commercially available systems, or in specific situations a custom version can be designed for the application. In the internal robot environment, a plurality of storage locations  18  are configured in an optimal manner for storage of substrate and/or substrate carriers  11  during process. These locations are equipped with product presence/absence sensors for verification. 
     The robot utilizes an automatic teaching sequence to map the work cell environment to avoid collisions when loading and unloading product as well as sensing product orientation so that the robot can properly pick up the product even if it is misaligned. The auto teach algorithm software is a commercially available software package, such as Cell Finder from Fanuc, which resides in the robot controller that is also a standard and commercially available item, such as model RJ3 from Fanuc. The software algorithm utilizes the robots motors for sensing torque. Analyzing the torque curve, the software detects any spikes in the torque curve, which results from increased output from the motor due to an opposing force that would result from a collision. The training sequence requires the robot to approach a plurality of operator defined points. 
     FIG. 16 shows the robotic stocking system interface to a process tool or front end automation system  50 . An object, a FOUP in the figure, exits the stocking system through an opening in the rear of the storage enclosure. The object is passed to the load port of another system which will use the object. 
     ELEMENTS AND REFERENCE NUMBERS 
       10  Storage Buffering System 
       11  Substrate/Substrate Carriers 
       12  6-axis Robot, Fanuc m6IB clean room class 100, w/motor covers 
       13  Robot Arm 
       14  End-Effector 
       15  Removable Service Robot Cart 
       16  Fanuc, Robot Controller 
       17  I/O Load Ports 
       18  Storage Location 
       20  Pivot Axis (End-Effector) 
       21  Pneumatic Gripper (End-Effector) 
       22  Robot Base 
       23  Attachment Arm (End-Effector) 
       24  Shoulder 
       25  Servo motor 
       26  Upper Arm 
       27  Pivot Shaft 
       28  Forearm 
       29  Actuator Arm 
       30  Wrist 
       31  Forearm centerline Axis 
       33  Casters, Removable Service Robot Cart 
       34  Kinematic Coupling, Removable Service Robot Cart 
       35  FOUP Shelf 
       36  Pneumatic Actuator, Magnetically couple 
       37  Fanuc, OP box Type-B, CE Mark 
       38  Sensor, Front sensing, convergent reflective 
       39  Kinematic Pin 
       40  Storage enclosure 
       42  Sliding door 
       43  Access door 
       50  Process tool or front-end automation