Abstract:
The invention relates generally to equipment for semiconductor wafer processing, for example, mechanisms and apparatus for handling pods or containers for housing silicon wafers or substrates. The pod may be a front-opening unified pod or similar article and may house a carrier or cassette for holding the wafers or substrates. Additionally, the invention relates generally to an automated system for transporting a plurality of wafers in the pod for processing, loading the pod on the receiving station, sealing the pod against an interface, opening the door of the pod, and shuttling the wafers into and out of a connected clean environment processing station, such as an ion implantation machine, using a robotic device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application incorporates by reference, and claims priority to, and the benefit of, U.S. Provisional Patent Application Serial Nos. 60/215,584, filed on Jun. 30, 2000, and 60/242,127, filed on Oct. 20, 2000. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The invention relates generally to equipment for semiconductor wafer processing, for example, mechanisms and apparatus for handling pods or containers for housing silicon wafers or substrates. In particular, the invention relates to pod door openers and related equipment used to remove and store the sealed pod door during wafer processing.  
         BACKGROUND INFORMATION  
         [0003]    The manufacture of integrated circuits (I.C.&#39;s) begins with blank, unpatterned semiconductor wafers. These wafers undergo a number of sometimes critical process steps before being formed into the final I.C. form. A substandard wafer can affect the number of usable I.C.&#39;s on a wafer, commonly referred to as yield. It is, therefore, desirable to have a machine for testing wafers to ensure the wafers meet a customer&#39;s standards and to maximize wafer yield.  
           [0004]    The testing of wafers is often accomplished by an automated process, in which robots continuously handle and test the wafers. Robotic testing and handling tends to be more efficient than manual testing and handling of wafers, since robots can be much faster, more precise, and less contaminating than human operators when handling wafers. In wafer handling processes, wafers are typically transported using carriers such as wafer cassettes or wafer pods. Pods differ from cassettes in that the pods typically are sealed to prevent contamination of the wafers enclosed therein.  
           [0005]    Previously, wafers having a diameter of 200 mm or 8 inches were commonly used in the semiconductor industry for the manufacture of I.C.&#39;s. More recently, 300 mm or 12-inch diameter wafers have been introduced to allow a greater number of integrated circuits to be produced from one wafer, thus lowering the cost of producing the I.C.&#39;s. New equipment and procedures have been developed to handle and process these new, larger wafers. For example, new larger, standard wafer pods, commonly referred to as Front Opening Unified Pods (FOUPs), have been developed. These sealed pods provide a contamination-free storage and transport environment for the wafers. To unload the wafers, the pod is positioned so that the wafers are oriented horizontally, the front door of the pod is opened to a contamination-free environment inside the testing equipment, and a robot end-effector is used to remove a wafer for processing or testing. Other versions of pods are used for smaller sized wafers; for example, Standard Mechanical Interface (SMIF) pods are typically used for 5-inch, 6-inch, and 8-inch wafers.  
           [0006]    This application incorporates by reference in their entirety the disclosures of the following U.S. Pat. Nos.: 6,071,059 Loading and Unloading Station for Semiconductor Processing Installations; 6,053,688 Method and Apparatus for Loading and Unloading Wafers from a Wafer Carrier; and 5,772,386 Loading and Unloading Station for Semiconductor Processing Installations.  
         SUMMARY OF THE INVENTION  
         [0007]    The current state of the art consists of complex pod door openers that require a large spatial working volume. The invention described herein is electromechanically novel, compact, highly reliable, and requires a minimal spatial volume to perform the same functionality as current state of the art systems. For example, the pod door opener is used for removing and storing the pod door during wafer processing, permitting loading and unloading of the 300 mm wafers relative to the pod. The pod requires the use of an apparatus to dock (or undock) the pod, unlatch (or latch) the sealed door, and to hold the pod securely during processing of the wafers. Further, the pod door opener provides a standard interface for mounting the pod to the wafer processing equipment. Semiconductor Equipment and Materials International (SEMI) standards control the mechanical interface requirements to maintain interchangeability and compatibility between pod manufacturers and processing equipment suppliers.  
           [0008]    Various embodiments of the invention are depicted in the configuration, layout, and design of the equipment and systems described and illustrated in the accompanying figures. The invention provides an efficient, unique, compact, highly reliable pod door opener (PDO). A PDO, in accordance with the invention, is less complicated and more reliable than conventional PDOs, operating within a significantly smaller total work volume by axially retracting and lowering the pod door, instead of pivoting the pod door about a transverse axis and then lowering the door.  
           [0009]    This fully automated system receives conventional semiconductor wafer sealed pods containing up to thirteen or twenty-five wafers, the pod doors incorporating two 90 degree door latches. A robot or other transport device deposits the pod onto a seating plate of the receiving station, which interfaces with a clean room of a semiconductor wafer processing tool, typically under positive pressure to prevent the ingress of contaminants. A locking mechanism locks the pod to the receiving station and pneumatic cylinders or other actuators may be employed to move the pod in a transverse direction to seal the pod against the interface plate and unlock and retract the pod door. A mechanical lead screw and ball nut or other transmission mechanism may be employed to lower the door to provide access for a robotic wafer handler to remove the wafers for processing and thereafter replace the wafers in the pod. The invention can be retrofitted and used in current, conventional semiconductor wafer processing systems providing enhanced reliability and smaller total operating volume.  
           [0010]    In one embodiment, the pod is presented to an interface plate of the apparatus, often referred to as a FIMS (front opening interface mechanical standard) plate by those skilled in the art. The pod is seated on a three pin kinematic mount and locked into place using a centrally disposed pneumatically driven rotary latch once one “presence” and three “in-place” sensors indicate the pod is properly located. The pod is translated and sealed against the processing equipment interface plate using a compact pneumatic cylinder, which is maintained under pressure until the pod is to be retracted. Suction cups with integral locating pins interface positively with the pod door. Once sealed, the pod door is unlatched using a flat pack single pneumatic cylinder to drive a dual output, double acting scotch yoke. A pneumatic cylinder, riding on linear carriage ways, then retracts the door horizontally. A vertically disposed electrical optic sensor confirms that the wafers have not extended beyond the plane of the door and then the door is lowered along the vertical or Z axis, driven by an electric DC servo motor, belt, and centrally disposed lead screw. Advantageously, the electrical and pneumatic control systems may be mounted on the pod side of the interface, to facilitate troubleshooting and repair, as required.  
           [0011]    In one aspect, the invention relates to a pod door opener including a door opening mechanism, a bulkhead having a seal plane and defining an aperture through which the door of a pod passes when removed by the door opening mechanism, and a work volume for the door opening mechanism. The work volume has a height, width, and depth, and the depth does not exceed about 80 mm from the seal plane. In various embodiments, the width does not exceed about 400 mm, generally horizontally centered on the seal plane, and the height does not exceed about 439 mm, generally vertically centered on the seal plane. In further embodiments, the pod door opener is configured to mount to a semiconductor wafer processing tool that permits a work volume for the door opening mechanism to have a depth of up to about 100 mm and/or a width of up to about 414 mm. Also, the bulkhead can be of a monocoque type construction.  
           [0012]    The door opening mechanism moves the pod door in a horizontal direction and a vertical direction and may include a door retraction device. The door retraction device includes a bidirectional propulsion device, such as an electromechanical system, an hydraulic system, a pneumatic system, or combinations thereof. The door opening mechanism may also include a vertical positioning system. The vertical positioning system can include a lead screw, a conformal rolling nut, and a motor. The vertical positioning system could also be a guided telescopic lift device, a linear electric motor, a cam driven system, an hydraulic actuator, a pneumatic actuator, a cable drive system, a magnetically coupled device, or combinations thereof.  
           [0013]    In still other embodiments, the pod door opener can include optionally a pinch avoidance system, a door key latch mechanism for grasping the pod door, and apparatus for sensing the presence and/or placement of the pod. The pinch avoidance system detects an obstruction and can include a frame coupled to the bulkhead and at least one switch disposed between the frame and the bulkhead. The door key latch mechanism includes a door interface plate coupled to the pod door opener, at least one door key latch coupled to the interface plate, a bi-directional propulsion device coupled to the interface plate, and a yoke coupled between the door key latch and the bi-directional propulsion device. The yoke translates a linear motion from the bidirectional propulsion device to a rotary motion on the door key latch. The bi-directional propulsion device can be an electromechanical system, an hydraulic system, a pneumatic system, or combinations thereof. The apparatus for sensing placement and position of the pod can include, for example, at least one flag and at least one sensing devices, such as be a proximity switch, a limit switch, an optical sensor, or similar device.  
           [0014]    In another aspect, the invention relates to a kinematic tool interface system for use with a pod door opener. The kinematic tool interface system includes a lower interface, at least one kinematic pin, and a seismic anchoring device. The lower interface includes a kinematic shelf and at least one support bracket. The kinematic shelf and support bracket can be coupled rigidly to a wafer processing tool. The kinematic pin is disposed on the kinematic shelf and is independently adjustable with a range sufficient to accommodate pitch, roll, and yaw adjustments to the pod door opener. The seismic anchoring device is disposed through an underside of the kinematic shelf. In one embodiment, the kinematic tool interface system includes at least one upper interface for securing the pod door opener to the wafer-processing tool.  
           [0015]    These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings in which:  
         [0017]    FIGS.  1 A- 1 C are isometric views of a prior art pod door opener;  
         [0018]    [0018]FIG. 1D is a side view of the prior art pod door opener of FIGS.  1 A- 1 C;  
         [0019]    FIGS.  2 A- 2 B are schematic top and side views of one embodiment of a pod door opener in accordance with the invention;  
         [0020]    [0020]FIG. 2C is a schematic view of a seal plane of the embodiment of the pod door opener shown in FIGS.  2 A- 2 B;  
         [0021]    [0021]FIG. 3 is an isometric view of the pod side of another embodiment of a pod door opener in accordance with the invention;  
         [0022]    [0022]FIG. 4 is an isometric view of the equipment side of the pod door opener of FIG. 3;  
         [0023]    FIGS.  5 A- 5 D are isometric views of a pod latching and drive system in accordance with the invention;  
         [0024]    FIGS.  6 A- 6 B are isometric views of a pod door chucking and retraction system in accordance with the invention;  
         [0025]    [0025]FIG. 6C is a cross-sectional view of one door key latch of FIG. 6A taken along line  6 C- 6 C;  
         [0026]    [0026]FIG. 7 is an isometric view of a vertical positioning system in accordance with the invention;  
         [0027]    [0027]FIG. 8A is schematic view of an operator pinch avoidance system in accordance with the invention;  
         [0028]    [0028]FIG. 8B is a cross-sectional view of the operator pinch avoidance system of FIG. 8A taken along line  8 B- 8 B;  
         [0029]    FIGS.  9 A- 9 B are isometric views of one embodiment of a kinematic tool interface system in accordance with the invention;  
         [0030]    [0030]FIG. 9C is a cross-sectional view of an upper interface of the kinematic tool interface system of FIGS.  9 A- 9 B taken along line  9 C- 9 C;  
         [0031]    [0031]FIG. 9D is an enlarged schematic view of the upper interface of the kinematic tool interface system of FIGS.  9 A- 9 C; and  
         [0032]    FIGS.  10 A- 10 H are wiring diagrams for various components of a pod door opener in accordance with the invention. 
     
    
     DESCRIPTION  
       [0033]    One tool for use with contamination-free handling of wafers is a load port, also referred to herein as a pod door opener (PDO). The load port allows a wafer carrier or pod to dock to a wafer processing tool while providing a continuous, clean environment for wafers as they are unloaded from the pod by an end-effector mechanism. One typical example of a prior art load port is illustrated in FIGS.  1 A- 1 C. In FIG. 1A, load port mechanism  10  includes a panel  11  having an equipment side  12  and a pod side  14 . On the pod side  14  of panel  11 , a pod  16  is positioned on an unloading station  18  and includes one or more wafers. In some embodiments of load port mechanisms, additional pods can be loaded in the mechanism  10  and can each be moved into the unloading position once the wafers of pod  16  have been unloaded, processed, and tested.  
         [0034]    On the equipment side  12  of panel  11 , the load port mechanism  10  includes an opening  22  in panel  11 , which has approximately the same dimensions as a front door  24  of the pod  16 . The front door  24  is aligned with the opening  22 , whereby contamination is prevented from entering the clean environment on the equipment side  12  by exerting positive air pressure inside the clean environment. Pod front door  24  includes several fastening mechanisms  26 , such as registration pins, door key latches, vacuum fasteners, and optionally, purge ports for the introduction/withdrawal of gases from the pod  16 .  
         [0035]    The load port mechanism  10  also includes a door removing mechanism  30 , which includes a plate  32  and a support rod  34 . The plate  32  and rod  34  are shown in a lowered position in FIG. 1A. FIG. 1B illustrates the load port mechanism  10  of FIG. 1A with the door removing mechanism  30  moved into position to remove the front door  24  of the pod  16 . Plate  32  has been raised by support rod  34  by motors or other mechanisms to the level of door  24  and opening  22 . The plate  32  and rod  34  are then moved toward the opening  22  and plate  32  is inserted into the opening to engage the door  24 . Plate  32  includes components that mate with the fastening mechanisms  26  on the front door. For example, plate  32  can include apertures into which pins on door  24  fit, door key latches to unlock a latch securing the door, etc. In some embodiments, vacuum pressure can be used to assist the plate  32  in mating with door  24 .  
         [0036]    [0036]FIG. 1C illustrates the prior art load port mechanism  10  after the door removing mechanism  30  has removed the front door  24  from the pod  16 . The plate  32  and rod  34  are tilted back angularly from the inserted position of FIG. 1B, where the door  24  is attached to plate  32  requiring a very large work volume. See FIG. 1D. The plate  32  and door  24  are then lowered to the position shown in FIG. 1C. Since the wafers in pod  16  are now accessible through opening  22 , a robot having z-axis movement such as handler arm  36  and end-effector  38  can be used to remove one or more wafers, one at a time, and transport the wafers to another testing or processing station inside the clean environment. The pod  16  remains stationary as the robot is moved to different elevations to take out the wafers. The robot loads the wafers into the pod in the same way that the wafers are unloaded after the wafers have been tested or processed.  
         [0037]    For purposes of semiconductor wafer processing with a pod, it is important to have a system that can remove and replace automatically the sealed door of the pod. In the prior art systems, the physical size and complexity of the pod door opener are cumbersome to the end user and prone to malfunction and failure. Additionally, installation and alignment of prior art systems to wafer processing equipment are difficult. The present PDO has been developed to minimize weight and spatial volume requirements. It is also simpler to install and align to semiconductor manufacturing equipment. All major subsystems have been developed in a modular fashion, which reduces the overall complexity of the semiconductor wafer processing equipment.  
         [0038]    FIGS.  2 A- 2 B depict top and side views, respectively, of a PDO  40  in accordance with the invention. In the figures, the PDO  40  is attached to a wafer processing tool  46  by a bulkhead  42 . A pod  44  is shown installed on the PDO  40 . The PDO  40  includes a variety of equipment and subsystems that operate to open and remove a door from the pod  44 . In part due to the modular design, the aforementioned equipment and subsystems operate within a reduced work volume  48 , as compared to prior art systems. The work volume  48  has a depth (X), a width (Y), and a height (Z). The work volume is measured from a seal plane  50 , which is the side of the bulkhead  42  that interfaces with the wafer processing tool  46 . The seal plane  50  is illustrated in FIG. 2C.  
         [0039]    In the embodiment illustrated in FIGS.  2 A- 2 C, the maximum work volume  48  dimensions are as follows: X=80 mm, Y=400 mm, and Z=439 mm. The additional dimensions shown are approximate and are for illustrative purposes only. Apparatus dimension greater than or less than these dimensions are considered to be within the scope of the invention. Additionally, several of the dimensions are given relative to a horizontal datum plane, a facial datum plane, a docked facial datum plane, and/or a bilateral datum plane. Generally, the horizontal datum plane is a horizontal plane that projects from the kinematic coupling pins on which the pod sits, the facial datum plane is a vertical plane that bisects the wafers and is parallel to the front side of the pod, the docked facial datum plane is the same as the facial datum plane, but with the pod in the docked position, and the bilateral datum plane is a vertical plane that bisects the wafers and is perpendicular to both the facial and horizontal datum planes. These datum planes are further described in SEMI standards nos. SEMI E92-0200E Provisional Specification for 300 mm Light Weight and Compact Box Opener/Loader to Tool-Interoperability Standard (Bolts/Light), SEMI E15-0698 Specification for Tool Load Port, SEMI E15.1-0600 Provisional Specification for 300 mm Tool Load Port, and SEMI E57-0600 Provisional Mechanical Specification for Boxes and Pods Used to Transport and Store 300 mm Wafers, the entireties of which are hereby incorporated herein by reference.  
         [0040]    A system overview describing the operation of various aspects of the invention will be described next with respect to FIGS. 3 and 4. FIG. 3 illustrates the system components as viewed from the operator or pod side  53 . This is the side from which the pod  44  is loaded and unloaded. The bulkhead  42  acts as the primary structural member for the entire system and is durable and lightweight. The bulkhead  42  may be of a monocoque construction, such that the outer skin absorbs substantially all of the stresses to which the body is subjected. This typically entails the use of an outer structural frame with lightweight structural filler materials enclosed within a thin membrane. In one embodiment, the bulkhead  42  is a thin singular plate to which all subsystems and components are attached. The bulkhead  42  also provides a precise interface surface to the wafer processing tool  46 . This interface surface, or seal plane  50 , is best seen in FIG. 4 and prevents the migration of airborne contaminants from the operator or pod side  53  to the equipment side  51 .  
         [0041]    In normal operation, the pod  44  is placed on the three kinematic pins  54  by an operator or by an automated material handling system. A presence sensor  55  and a series of three placed sensors  56  verify that the pod  44  is both present and correctly placed on the kinematic pins  54 . Once verified, further system motion is allowed. First, a pod latch  57  is actuated to hold the pod  44  in place on the kinematic pins  54 . The pod latch  57  holds the pod  44  and its contents, the silicon wafers, securely during processing. After latching, the pod  44  is moved to a docked position against the bulkhead  42  by a pod drive  58 . The bulkhead  42  has an integral rim feature that provides a sealing surface  61  for the pod enclosure  44 . This sealing surface  61  is used to prevent the migration of airborne contaminants from reaching the contents of the pod  44 . As the pod  44  docks, door pins  59  and door key latches  60  engage with corresponding features in the removable pod door. The door pins  59  provide positional accuracy and repeatability, which ensures proper chucking of the pod door. The door key latches  60  are rotated and the pod door is ready for removal from the pod  44 . Vacuum suction is provided coaxially about the door pins  59  by suction cups  62 , which aid in the door chucking process. Once the pod door is properly chucked, the door is retracted from the pod  44  and is lowered into a position that does not interfere with the wafer transfer robotic apparatus. Once the wafer transfer process is complete, the reverse order of events occurs such that the pod  44  is ready for removal from the PDO  40 . Further, the compact nature of the invention allows for sufficient internal volume to provide modular control components. An access door  52  provides the required accessibility to all control system components.  
         [0042]    All pod motions as well as the presence and placement functions are managed by a pod drive  58 . FIGS.  5 A- 5 D illustrate the pod drive  58  and its components. The pod drive housing  64  provides structural support for the associated drive components and payload, as well as a rigid and precise coupling to the bulkhead  42 . The pod  44  is placed on a series of kinematic pins  54 . Three kinematic pins  54  are shown; however, the number and position of the kinematic pins  54  may vary to suit a particular application. The kinematic pins  54  are rigidly attached to a support plate  65 , which moves in a fore and aft direction to accomplish pod  44  docking and undocking functions. The fore and aft motions are accomplished by a pair of linear bearing devices  66  (FIG. 5B) and a bi-directional propulsion device  67  (FIG. 5C). The bidirectional propulsion device  67  could be of electromechanical, pneumatic, or hydraulic form, for example a pneumatic actuator. A rigid coupling  68  connects the propulsion device  67  and the support plate  65 . Fore and aft travel distances are adjusted by stops  69  and energy absorption devices  70  (FIG. 5C). Sensing devices  76  are utilized to provide positional feedback to the control system. Sensing devices  76  can, for example, include proximity or limit switches.  
         [0043]    As previously noted, the pod latch  57  holds the pod  44  securely in place on the kinematic pins  54 . The pod  44  generally has provisions on the underside for holding, with a feature located at a forward portion thereof, near the removable door. Alternatively, the feature is centrally located. The pod latch  57  is rotated by a bi-directional propulsion device  71  that is rigidly coupled to the support plate  65  and could be of electromechanical, pneumatic, or hydraulic form. Several methods of clamping may be used, such as toggle clamps, spring plates and roller devices, cam driven arms, or a rotary pull down device. In the embodiment illustrated in FIG. 5D, a rotary pull down device  63  is used. The rotary pull down device  63  includes the previously mentioned propulsion device  71 , which is coupled to the pod latch  57 . A coaxial ring  72  is placed over the lower portion of the pod latch  57  and has a radial and axial groove  100  about its periphery. A following device  73  is attached to the pod latch  57  and is guided within the groove  100 . A return spring  74  is used to ensure that the pod latch  57  returns to its initial position. When the pod latch  57  is in its unlatched state, the rotary pull down device  63  positions the pod latch  57  in its uppermost position. During the latch cycle, the rotary pull down device  63  positions the pod latch  57  in its lowermost, or clamped, position. The pod latch  57  also has an integral flag  75  control system which, in conjunction with sensing devices  101 , provides positional feedback to the system.  
         [0044]    The door chucking and retraction system  103 , as illustrated in FIGS.  6 A- 6 C, includes three primary structural members and an assemblage of components to provide the desired motions. The door interface plate  77  is a thin-walled structural element used to support the door latching and vacuum suction components. The support beam  79  is a structurally rigid member used to support the door interface plate  77 . The carriage  78  is the third structural member and couples the door chucking and retraction system  103  to a vertical positioning system  104 .  
         [0045]    As previously mentioned, the door chucking process involves the use of two rotary door key latches  60 , which are used to engage or disengage the removable pod door. The door key latches  60  are rotated by a bidirectional propulsion device  76  that is rigidly coupled to the door interface plate  77  and could be of electromechanical, pneumatic, or hydraulic form. A modified scotch yoke translates the linear motion of the propulsion device  76  into the desired rotary latch motion. The door key latch  60  is a precision component that rotates freely in a rigid bearing  80  that is fixed to the door interface plate  77 . Attached to the end of the door latch key  60  is a yoke  81 , which has an integral flag  82  that, in conjunction with a sensing device  83 , provides positional feedback. A lever arm  84  is used to couple the propulsion device  76  to the yoke  81 . The lever arm  84  has an attached following device  85  that is disposed in a slot  90  in the yoke  81 . An adjustable stop  86  is utilized to limit the phase of rotation of the door key latch  60 .  
         [0046]    As shown in FIG. 6A, two door alignment pins  59  are utilized. As previously described, the door pins  59  engage with corresponding features in the removable pod door. In one embodiment, the door chucking and retraction system  103  uses two pins  59 , one acting as a primary orientation pin and the other as a secondary orientation pin; however, the number and location of the pins  59  may vary, as necessary to mate with the pod  44 . As shown in FIG. 6C, the pins  59  are removable and are secured by a coupling  87 . The coupling  87  is hollow in nature and provides an unimpeded path for vacuum to reach the suction cup  62 . Vacuum leakage is prevented by a seal  88  between the coupling  87  and a support  89 , which is precisely oriented in door interface plate  77 . Vacuum may be supplied in a number of ways, for example by using a compact venturi device  90 , which is located proximate the suction cup  62 . Alternatively, vacuum may be supplied by a pumping device.  
         [0047]    Door retraction is accomplished by a bi-directional propulsion device  91  that is rigidly coupled to the support beam  79  and could be of electromechanical, pneumatic, or hydraulic form. A yoke  92  is rigidly attached to the end of the propulsion device  91  and has attached following devices  93  that are guided by slots  99  in side supports  94 . The support beam  79  is allowed to translate in a horizontal plane (arrows A-A) by a pair of linear bearings  95  that are attached to the carriage  78 . A link  96  connects the yoke  92  to the carriage  78  by bearings  97 , thereby enabling motion to occur only in the horizontal plane. Fore and aft travel distances are limited by stops  98 . This system effectively converts a vertical translation into a horizontal translation, without the need for complex gearing or other apparatus.  
         [0048]    Once retracted, the door  77  can be lowered to a stored position so that the door  77  does not interfere with a robotic wafer transfer apparatus. One embodiment of a vertical positioning system  104  is illustrated in FIG. 7 and is used to raise and lower the door chucking and retraction system  103  along a vertical axis  126 . The system  104  is rigidly attached to the bulkhead  42  by an upper bearing housing  105  and a lower bearing housing  106 . The upper bearing housing  105  holds a supporting bearing  107  for the upper end  108  of a leadscrew device  109 . The lower bearing housing  106  holds a pair of precision bearings  110 , which provide rigidity in both the axial and radial directions.  
         [0049]    The door chucking and retraction system  103  is coupled to the vertical positioning system  104  by a rolling nut  111 . The rolling nut  111  is of a particular design, such that system misalignment is compensated for by a plurality of elastomeric bushings  112 . The elastomeric bushings  112  also contribute to smooth motion. A pair of linear bearings  113  are attached to the bulkhead  42  to provide a smooth, guided motion. The carriage  78  is coupled to the linear bearings  113  by a clamp plate  114 . The vertical positioning system  104  is driven by a bidirectional rotary propulsion device  115 , which could be of electromechanical, pneumatic, or hydraulic form.  
         [0050]    In one embodiment, the device  115  is a precision electric motor with an in-situ control  116 . A holder  117 , such as an electromechanical brake, is attached to the motor shaft to prevent any undesired motion from occurring. The motor  115  is supported by a plate  119 , which is rigidly attached to the bulkhead  42 . Motor torque is transmitted to the leadscrew  109  by a toothed drive belt  120  and pulley system  121 . Proper belt tension is accomplished by adjustment of a sliding plate  122  and guided springs  123 . Position verification is accomplished by use of a flag  124 , which is rigidly attached to the clamp plate  114 . Sensors  125  are used to determine the presence of the flag  124 .  
         [0051]    Several alternative techniques are possible to perform the desired functions of the vertical positioning system. Among these are a guided telescoping lift device, other linear propulsion devices, such as linear electric motors, magnetically coupled devices, cables or straps guided by pulleys and controlled with counterweights, cam driven systems, and hydraulic or pneumatic actuators.  
         [0052]    In order to prevent an operator from becoming pinched by the pod docking motion, a pinch avoidance system  130  is provided. FIG. 3 illustrates the orientation of the pinch avoidance system  130  as implemented on the PDO  40 . FIG. 8A illustrates one embodiment of the pinch avoidance system  130 . The system  130  includes a lightweight frame  131  that circumscribes the pod docking opening  143  within the bulkhead  42 . If an object should become trapped between the pod  44  and the frame  131  when the pod  44  is being advanced, the frame  131  is pushed toward the bulkhead  42  and a series switch circuit  132  opens. In one embodiment, there are four switches  133  located about the frame  131 , such that a force applied at any point along the frame  131  will open the switch circuit  132 . The quantity and location of the switches  133  can be varied to suit a particular application. The pod docking motion is reversed immediately upon the switch circuit  132  changing to an open state.  
         [0053]    The pinch avoidance system  130  includes a number of components. The frame  131  is attached to the bulkhead  42  by a plurality of screws  134 , which provide rigid coupling to the bulkhead  42  as well as guidance for return springs  135 . As best seen in FIG. 8B, the switches  133  include a mounting plate  136  rigidly attached to the frame  131 , a spacer  137 , a spring plate  138 , and a bumper  139  which, when depressed, lifts the contact ring  140  off of the mounting plate  136 , thereby opening the circuit  132 . To facilitate manufacturability and maintain a low physical profile, switch pockets  141  and wiring channels  142  may be formed in the frame  131 .  
         [0054]    Another improvement over current state of the art pod door opening systems is the implementation of a kinematic tool interface system  150  that results in a greater degree of interchangeability when mounting or dismounting the PDO  40 . The kinematic tool interface system  150 , as illustrated in FIGS.  9 A- 9 D, includes an upper and lower interface  153 ,  151 . The lower interface  151  includes a kinematic shelf  152  and one or more support brackets  154 . In this embodiment, the system  150  includes two brackets  154 . The kinematic shelf  152  and support brackets  154  are rigidly coupled and are attached to a wafer processing tool  46  for structural support of the PDO  40 . Attached to the kinematic shelf  152  are a plurality of kinematic pins  156 . In this embodiment, the system  150  includes three kinematic pins  156 . The kinematic pins  156  are independently adjustable and have sufficient range to provide pitch, roll and yaw adjustments. A seismic anchoring device  158  is locked in place once adjustments have been completed.  
         [0055]    The upper interface  153  is a spherical adjusting device that conforms to the final position of the lower interface  151 . The upper interface  153  is depicted in FIGS.  9 C- 9 D, and includes an upper interface housing  160  retained in the bulkhead  42  by a wave washer  162  and a retaining ring  164 . In the illustrated embodiment, the upper interface  153  allows freedom of movement in the vertical plane (arrow B-B). Conformance to the lower interface  151  is enabled by a threaded adjuster  166 , which contacts a self-centering ring  168 . The ring  168  and housing  160  are adjusted by a cup  170 . The resultant interaction of these components allows the upper interface  153  to conform to the final pitch, roll, and yaw position of the lower interface  151 .  
         [0056]    FIGS.  10 A-H are wiring diagrams for various components of the pod door opener  40 . The wiring diagrams are for illustrative purposes only and will vary depending on the specific configuration of any particular component/system of the pod door opener  40 . FIG. 10A is a wiring diagram for a status display for use with a pod door opener  40 . FIG. 10B is a wiring diagram depicting the AC/DC power distribution of the pod door opener  40 . FIG. 10C is a PDO communications wiring diagram. FIG. 10D is a wiring diagram for a pneumatic interface for the various components/systems of the pod door opener  40 . FIG. 10E is a wiring diagram for the pinch avoidance system  143 . FIG. 10F is a wiring diagram for a FIMS plate. FIG. 10G is a wiring diagram for the pod drive plate  58 . FIG. 10H is a wiring diagram for the vertical positioning system  104 .  
         [0057]    Having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. The described embodiments are to be considered in all respects as only illustrative and not restrictive.