Abstract:
A compact pinlifter assembly is fitted in a substantially enclosed cavity within a wafer chuck such that an overall outside shape of the wafer chuck remains highly unaffected. The pinlifter assembly includes wedge guides providing a movement path in a wedge angle relative to the wafer holding face. A pin actuator is driven along the wedge guides transforming its movement along the wedge guides into a vertical movement of the lifting pins perpendicularly sliding between the cavity and the wafer holding face. The combination of wedge guides and pin actuator takes advantage of the relatively large lateral dimensions of the wafer chuck to move the pin actuator between end positions that are in a distance multiple of the pin lifters movement. Due to the wedge angle, the actuators comparatively large scale movement is transformed in a highly precise, smooth and balanced movement of the pin lifters.

Description:
CROSS REFERENCE  
       [0001]     The present application cross references the concurrently filed and commonly owned US Patent Application titled “Compact Wafer Handling System With Single Axis Robotic Arm And Prealigner-Cassette Elevator” by Marc Aho and Daniel Tran, which is hereby incorporated by reference.  
       FIELD OF INVENTION  
       [0002]     The present invention relates to pinlifter assemblies for lifting a wafer from and lowering a wafer onto a wafer chuck. Particularly, the present invention relates to pinlifter assemblies integrated within an outside diameter of a wafer chuck.  
       BACKGROUND OF INVENTION  
       [0003]     During wafer fabrication, wafers are commonly transferred between a wafer chuck and a robotic arm by mechanical devices along a dual positioning axis vertical to the chuck&#39;s wafer holding face. The mechanical devices lift/lower a wafer between the chuck&#39;s wafer holding face and a loading level, where the wafer may be accessed by a robotic arm for further transportation. Such mechanical devices that employ pins to contact the bottom side or the circumference of the wafer for transfer along the dual positioning axis are commonly referred to as pinlifter assemblies.  
         [0004]     A pinlifter assembly needs to be simple and compact while providing a smooth and balanced motion of each pin contacting the wafer. In addition, the pinlifter assembly needs to be designed around other features affiliated with the positioning and holding of the wafer. Such features may include vacuum systems for holding the wafer onto the wafer holding face and precision motion systems for moving the chuck together with the wafer. Such a motion system may be for example an X-Y stage or a rotary stage. All these limiting aspects need to be accounted for by the design of the pinlifter assembly. At the same time, the pinlifter assembly is desirably compact and highly integrated in the wafer chuck. The present invention addresses this needs.  
       SUMMARY OF INVENTION  
       [0005]     A compact pinlifter assembly is fitted in a substantially enclosed cavity within a wafer chuck such that an overall outside shape of the wafer chuck remains highly unaffected. The pinlifter assembly includes wedge guides providing a movement path in a wedge angle relative to the wafer holding face. A pin actuator is driven along the wedge guides transforming its movement along the wedge guides into a vertical movement of the lifting pins perpendicularly sliding between the cavity and the wafer holding face.  
         [0006]     The combination of wedge guides and pin actuator takes advantage of the relatively large lateral dimensions of the wafer chuck to move the pin actuator between end positions that are in a distance multiple of the pin lifters movement. Due to the wedge angle, the actuators comparatively large scale movement is transformed in a highly precise, smooth and balanced movement of the pin lifters.  
         [0007]     An actuator drive preferably employs a stepper motor, a reduction gear mechanism and a connecting rod transforming the rotational movement of the actuator drive into a linear movement of the pin actuator.  
         [0008]     The pin actuator provides recesses and a cutout for all involved components as well as for an eventual vacuum connect vertically propagating across the cavity. The cavity itself may be hermetically sealed and operate itself additionally as a vacuum connect. 
     
    
     DESCRIPTION OF THE FIGURES  
       [0009]      FIG. 1  is a perspective view of a wafer testing device with a wafer chuck in accordance with the preferred embodiment of the invention.  
         [0010]      FIG. 2  is a top perspective view of the wafer chuck of  FIG. 1 .  
         [0011]      FIG. 3  is a front view of the wafer chuck of  FIG. 1 .  
         [0012]      FIG. 4  is a bottom perspective view of the wafer chuck of  FIG. 1 .  
         [0013]      FIG. 5  is a bottom perspective view of the wafer chuck of  FIG. 4  with the base lid removed and showing the chuck cavity with mounted guide structures and pinlifters extending with their bottom faces into the cavity.  
         [0014]      FIG. 6  is a bottom perspective view of the wafer chuck of  FIG. 5  illustrating additionally the pin actuator, actuator drive and connecting rod.  
         [0015]      FIG. 7  is a top perspective view of guide structures, pinlifters, pin actuator and actuator drive in assembled position. 
     
    
     DETAILED DESCRIPTION  
       [0016]     In accordance to  FIG. 1 , an exemplary wafer testing device  1  may be a well known spectrometer, reflectometer or other well known wafer testing device in which a well known wafer is moved and positioned with high precision beneath and relative to a measurement head  42 .  
         [0017]     The wafer testing device  1  may have a housing  11  combined with a base  2 . The housing  11  may have any suitable configuration for providing structural support and for integrating additional well known components such as, for example, electrical and other supply devices, control computers and other devices that are well known parts of optical measurement devices.  
         [0018]     The base  2  holds a measurement assembly  4  which may include a head carrying arm  41  and the measurement head  42 . Attached to and carried by the base plate  2  is a stage system  3  including for example a high precision linear X-stage  31  and a high precision linear Y-stage  32 . X-stage  31  and Y-stage  32  may be combined in a single commercially available device. On top of the stage system  3  is a chuck  5  for receiving and fixedly holding a wafer (not shown) during measurement.  
         [0019]     Referring to  FIG. 2 , the chuck  5  may have a chuck body  51  featuring a wafer holding face  510 , which is fabricated with high planarity and smoothness for receiving and holding a wafer. The holding face  510  may be interwoven by communicating vacuum grooves  512  for distributing a vacuum across the holding face  510 . The vacuum may be used in a well known fashion to temporarily fix the wafer on the holding face  510 . The vacuum grooves  512  are accessed by a vacuum channel  513  that propagates across the chuck height CH (see  FIG. 3 ).  
         [0020]     The chuck body  51  further features at least three but preferably four pin channels  518  preferably concentrically arranged with respect to a center axis CA of the chuck  5 . The pin channels  518  are substantially perpendicular to the wafer holding face  510  and are correspondingly shaped to pinlifters  53  (see  FIGS. 5, 7 ). The pinlifters  53  are slide ably embedded in the pin channels  518  for lifting and lowering a wafer with respect to the wafer holding face  510 . Each pinlifter  53  has a top face  531  and a bottom face  532  (see  FIG. 5 ). In  FIG. 2 , the pinlifters  53  are shown in a bottom position, in which the top faces  531  are below the holding face  510 .  
         [0021]     As seen in  FIGS. 3, 4 , the chuck  5  has preferably a rotationally symmetric outside shape with an outside diameter OD that preferably corresponds to a diameter of a wafer intended to be placed on the chuck  5 . The majority of the chuck&#39;s  5  structure is contributed by the chuck body  51 . The chuck body  51  is preferably monolithically fabricated from a thermally stable and wear resistant material such as granite. The chuck  5  may have a base diameter BD that is recessed from the outside diameter OD. A base lid  52  may be attached at the bottom to the bottom of the chuck body  51  with lid screws  521 . A vacuum connect  515  may extend through the base lid  52  for connecting a vacuum to the vacuum channel  513 .  
         [0022]     As seen in  FIGS. 5, 6 ,  7 , a cavity  516  is placed below and structurally separated from the holding face  510 . The pin channels  518  extend between the holding face  510  and the cavity  516 . Embedded in the cavity is a pinlifter assembly including the wedge guides  542 , pin actuator  55  and driving members  56 ,  57 . The wedge guides  542  are preferably provided by guide structures  54  preferably attached in the cavity  516  via guide screws  545 . In  FIGS. 5, 6 , the guide structures  54  are shown as being attached to chuck body  51  but may be additionally and/or alternatively attached to the base lid  51 .  
         [0023]     The scope of the invention includes embodiments, in which the cavity  516  is at least partially provided by secondary structural components of a rotary stage, a single axis linear stage, a dual axis linear stage or any other movement device well known for precision positioning a wafer fixed to a chuck. In such embodiments, the lid  52  may be substituted by the secondary structural components. Also in such embodiments, the guide structures  54  may be attached to the secondary structural components. Particularly in the case of a rotary stage, the guide structures  54  may be attached to a non rotating portion of the rotary stage whereas the chuck body  51  is attached to a rotating portion of the rotary stage.  
         [0024]     In other embodiments, the wedge guides  542  may be formed into the chuck body  51  and/or the base lid  51  as integral part of the cavity  516 . In such cases, the guide structures  54  are omitted.  
         [0025]     The pin actuator  55  has sliding features  552  correspondingly shaped to the wedge guides  542  and is slide ably guided by said wedge guides  542 . The sliding features  552  may be configured in any well known fashion such as snuggly fitting profiles, line contacting glide pins or rollers.  
         [0026]     The pin actuator  55  has a rod connect  557  via which the pin actuator  55  receives a driving force from a connecting rod  57 . The connecting rod  57  in turn is hinged between the rod connect  557  and a motored rotating crank  567 . The rotating crank  567  is part of actuator drive  56 , which may preferably include a stepper motor and an optional reduction gear. In case where the stepper motor drives the rotating crank directly, actuator drive  56  includes the stepper motor alone.  
         [0027]     The stepper motor is particular suitable as a motoring device to be embedded inside a shallow cavity since it may be readily and commercially available in configurations with low extension along its rotation axis RA. In such case, the stepper motor may be embedded in the cavity with its rotation axis RA substantially perpendicular the holding face  510 .  
         [0028]     The scope of the invention includes embodiments, in which the pin actuator  55  may be alternatively driven by a gear rotated by the actuator drive  56  and engaging with a gear rack attached to the pin actuator  55 .  
         [0029]     The wedge guides  542  are preferably linear. In alternate embodiments, the wedge guides  542  may be circular and rotationally symmetric arranged such that the movement path is a rotation. In such case, the wedge guides  542  may be arranged such that a rotation axis of the movement path substantially coincides with the center axis CA. Also in such case, the gear rack described for embodiments in the paragraph above may be a conventional gear as may be well appreciated by anyone skilled in the art.  
         [0030]     The vacuum connect  515  protrudes across the cavity  516 . To avoid interference between the pin actuator  55  moving between its two opposing end positions, the pin actuator  55  has a cutout  555 . The pin actuator  55  may also have recesses  556  to avoid interference with driving members such as connecting rod  57  and actuator drive  56 . The pin actuator  55  may feature additional lateral actuator faces  551  that correspond to guide faces  541  for an eventual additional horizontal guiding of the pin actuator  55  along its movement path.  
         [0031]     The pinlifters  53  rest with their respective bottom faces  532  on a pin contact face  550  of the pin actuator  55  such that the pinlifters  53  are simultaneously moved along pin channels  518  and the top faces  531  are moved between a bottom position below the holding face  510  and a top position above the holding face while the pin actuator  55  is moved along the movement path. The pinlifters  53  may rest spring loaded and/or gravity loaded on the contact face  550 .  
         [0032]     The top position preferably corresponds to a loading level at which the wafer may be accessed from beneath by a robotic arm for further transfer away from the chuck  5 . For that purpose, the pinlifters  53  may be lowered again once the robotic arm is in loading position such that the weight of the wafer is transferred from the top faces  531  onto the robotic arm. Likewise and in an opposite sequence of steps, the pinlifters  53  may be moved into their top position while a wafer is held in position above the wafer holding face  510 . The pinlifters  53  may be moved by locically and/or computerized controlled powering the actuator drive  56  in a well known fashion. Within a wafer testing device  1  such as described in the concurrently filed and cross referenced application titled “Compact Wafer Handling System With Single Axis Robotic Arm And Prealigner-Cassette Elevator” the pinlifter  53  movement may be defined as a movement along dual positioning axes DP. In such testing device  1 , the controlled powering may be accomplished by a control system of the testing device  1 .  
         [0033]     In the preferred embodiment, the pin contact face  550  is substantially coplanar with the holding face  510  while the pin actuator  55  is moving along the movement path. In alternate embodiments, the wedging effect between the pin actuator  55  and the pin lifters  53  may be provided by the pin contact face  550  tilted with the wedge angle WA relative to the pin actuator&#39;s  55  movement path. In such alternate case, the pin actuator  55  may be moved substantially horizontally.  
         [0034]     In another embodiment, the cavity  516  may be substantially sealed such that a vacuum may communicate substantially unimpeded across the cavity  516 . In that case, the vacuum connect  515  may extend from the cavity&#39;s  516  bottom and the core of the cavity  516  may remain free of any vacuum transmission structure that may limit the design of the pinlifter assembly.  
         [0035]     Accordingly, the invention described in the specification above is set forth by the following claims and their legal equivalent: