Abstract:
An end effector having a paddle adapted for mounting to a robot arm. On the top side of paddle are two finger housings spaced apart and in opposed relationship. In the preferred embodiment, one of these finger housings is slideable along the paddle while the other is fixed. Mounted to the outer surfaces of these finger housings are finger assemblies for gripping a wafer on its edge and configured to assist in the transfer of the wafer from the end effector to some other device. Finger housings with finger assemblies can also be mounted to the bottom surface of the paddle, allowing the end effector to carry two wafers at one time. Methods for handling and transferring wafers using these end effectors are also disclosed.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to the transfer of articles, such as semiconductor wafers, and more particularly to an end effector that grips a wafer on its edge and a method for handling and transferring very thin semiconductor wafers.  
         BACKGROUND OF THE INVENTION  
         [0002]    The use of robot arms is a well established manufacturing expedient in applications where human handling is inefficient and/or undesired. For example, in the semiconductor arts robot arms are used to handle wafers during various process steps. Such process steps include chemical-mechanical planarization (CMP), etching, deposition, passivation, etc., where a sealed environment must be maintained to limit the likelihood of contamination and to ensure that various specific processing conditions are provided.  
           [0003]    Current practice includes the use of an end effector (also known as a robot blade) attached to robot arms to load semiconductor wafers from a loading port into various processing ports within a multiple chamber process system. The robot arms are then employed to retrieve the wafer from a particular port after processing within an associated process chamber. The wafer is then shuttled by the robot arms to the next port for additional processing. When all processing within the system is complete, the robot arm returns the semiconductor wafer to the loading port and the next wafer is placed into the system by the robot arm for processing. Typically, a stack of several semiconductor wafers is handled in this manner during each process run.  
           [0004]    Typical wafer handlers hold the wafer on its bottom side using backside suction generated by the wafer handler. Alternatively, some wafer processing machines use a suction from the device receiving the wafer to pull the wafer from the wafer handler. However, the application of a mechanical apparatus and action to the top or device side of the wafer may damage or contaminate the wafer.  
           [0005]    Accordingly there is a need for an end effector that is capable of gripping a silicon wafer on its edge and a method for handling and transferring very thin semiconductor wafers. Additionally there is a need for an end effector that can grip more than one wafer at a time.  
         SUMMARY OF THE INVENTION  
         [0006]    An object of the present invention is to provide an end effector that is capable of gripping a silicon wafer on its edge.  
           [0007]    Another object of the present invention is to provide an end effector that is capable of carrying multiple wafers at one time.  
           [0008]    Yet another object of the present invention is to provide a method for handling and transferring very thin semiconductor wafers.  
           [0009]    The present invention meets these objectives by providing an end effector having a paddle adapted for mounting to a robot arm. On the top side of the paddle are two finger housings spaced apart and in opposed relationship. In the preferred embodiment, one of these finger housings is slideable along the paddle while the other is fixed. Mounted to the outer surfaces of these finger housings are finger assemblies for gripping a wafer on its edge. The finger assemblies are also configured to assist in the transfer of the wafer from the end effector to some other device. Finger housings and finger assemblies can also be mounted on the bottom side of the paddle enabling the end effector to carry two wafers at one time.  
           [0010]    In operation, once the wafer is mounted to the end effector contemplated by the present invention, the robot brings the end effector to the device to which the wafer is to be transferred. The wafer is brought within the influence of suction generated in the device. The device then engages the finger assemblies so that the end effector&#39;s grip is released. Concurrently, the finger assemblies gently push the wafer towards device enabling the suction force to pull the wafer to the device. The end effector can then be rotated 180 degrees and this process is then repeated for a wafer is mounted on the bottom side.  
           [0011]    By gripping the wafer on the edge damage to the top and bottom of the surfaces is avoided. Further, the twist effect of the finger assemblies that assists in transferring the wafer to the device reduces the magnitude of the required suction, thus avoiding further damage to the wafer.  
           [0012]    These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a top perspective view of the end effector contemplated by the present invention.  
         [0014]    [0014]FIG. 2 is an overall perspective view of an alternative embodiment of the end effector contemplated by the present invention.  
         [0015]    [0015]FIG. 3 is a partial cross-sectional view taken along line  3 - 3  of FIG. 1.  
         [0016]    [0016]FIG. 4 is a perspective view of the end effector of claim  1  with a wafer mounted on it. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring to FIG. 1, an edge gripping end effector is generally denoted by reference numeral  10 . The bottom and top of the end effector  10  are structurally and functionally identical allowing the end effector  10  to hold two wafers at one time. One wafer on its top side and one wafer on its bottom side. For purposes of clarity the following describes the top side of the end effector  10  but the description also applies to the bottom side.  
         [0018]    The end effector  10  includes a flat plate  12  also referred to as a paddle that extends from a first end  14  to a second end  16 . The thickness of the paddle  10  is on the order of 6 to 12 mm. The first end  14  has a plurality of holes  18  that are used, in a manner familiar to those skilled in the art, to couple the end effector  10  to a robot arm, (not shown). Moving from the first end  14  to the second end  16 , mounted on the paddle  12  is an actuator support  20  to which is mounted a commercially available pneumatic actuator  22 . The actuator  22  receives air from a source not shown through port  24 . In response to pressurized air flowing through port  24 , the actuator  22  causes a connector  26  to extend (i.e. move forward toward end  16 ) or retract (i.e. move backward toward end  14 ). The connector  26  is coupled to one end of a slider or linear bearing  28  by a pin or screw  30 . The slider or linear bearing  28  rests on the surface of the paddle  12  and at its second end is connected to a slideable finger housing  32 . The linear bearing  28  is a commercially available bearing having a fixed portion connected by screws to the paddle and slideable portion mounted to the fixed portion which is coupled to the finger housing  32 .  
         [0019]    The slideable finger housing  32  generally has an arcuate shape that matches the shape of the outer edge of the wafer and also has an inward facing sloped or tapered surface  34 . The housing  32  also has at least one threaded hole  36  for receiving a finger assembly  50  which will be described in detail later in this application. In the preferred embodiment, there are four threaded holes  36  equally spaced along the top surface of the slideable finger housing  32 . It should be appreciated that the number of threaded holes  36  and their spacing may vary with different embodiments of the present invention.  
         [0020]    A fixed finger housing  40  is connected to the end  16  of the paddle  12 . This assembly  40  does not move. Like the slideable finger housing  32 , the fixed finger housing  40  has an arcuate shape that matches the shape of the outer edge of the wafer and also has an inward facing arcuate sloped or tapered surface  44  that is opposed relation to surface  34 . In the preferred embodiment, the housing  40  has three threaded holes  46  for receiving in each hole a finger assembly  50  which will be described in detail later in this application. It should again be appreciated that the number of threaded holes  46  and their spacing may vary with different embodiments of the present invention. FIG. 2 shows the bottom side of an alternative embodiment  10   a  where the only difference is the number of holes  36 ,  46 . In this embodiment, the slideable finger housing  32  has six threaded holes  36  and fixed finger housing  40  has a single threaded hole  46 . It should further be appreciated that the number of holes on the slideable finger housing may be less than the number of holes on the fixed finger housing.  
         [0021]    Referring to FIG. 3, the threaded hole  36  has two tiers. A first tier  37  at a first depth from the surface and a second tier  39  extending further inward from the first tier and centered relative to the first tier. The threaded holes  46  are identical to the hole  36 . Disposed within the hole  36  is the finger assembly  50 . The finger assembly  50  is comprised of a bellows cup  52  having an annular fitting  53  and a annular resilient member  55 . The bottom of the resilient member  55  rests on the first tier  37  and the top extends outward and beyond the hole  36 . The fitting  53  has a threaded outer surface portion that engages the threads  56  disposed on the surface of the hole  36  just below the tier  37 . Above the tier  37 , the fitting  53  is not threaded and extends into a counterbore in the resilient member  55 . The resilient member  55  is preferably made of a resilient rubber like material such as Urethane, Nitrile, Silicone, Flourocarbon, and Neoprene and is press fit onto the fitting  53 . Disposed through the bellows cup  52  is a rod or pin  62 . The base portion  63  of the pin  62  has a diameter that is greater than the diameter of the fitting  53  and the remainder of the pin  62 . A spring  60  is mounted between the bottom of the base portion  63  and the second tier  39  of the hole  36 .  
         [0022]    Referring to FIG. 4, in operation the end effector  10  is initially positioned with the slideable finger housing  32  retracted and the surfaces  34 ,  44  spaced apart so that a standard size wafer  70  will rest on the surfaces  34 ,  44 . The slideable finger assembly  32  is then extended towards the fixed finger assembly  40 . This movement of the slideable finger assembly  32  pushes the wafer  70  outward along the surfaces  34 ,  44  until the wafer  70  rests on the top surface of the inner portions  56  with its edge  72  embraced against the rods or pins  62 . The rods or pins  62  exert a compressive force on the edge  72  of the wafer  70  so as to hold it in place even when the end effector  10  is rotated 180 degrees from the top position.  
         [0023]    When the wafer  70  needs to be transferred, for example, to a polishing pad, this is usually accomplished by a slight suction on the pad side which pulls the wafer  70 . The wafer  70  must be in the up position. To avoid damaging the wafer  70 , the suction is as weak as permissible while still being able to pull the wafer. The subject invention assists in this transfer in the following manner and thereby reduces the magnitude of the required suction. As the wafer  70  is brought near the pad, the structure holding the pad will push down on the rods or pins  62  causing them to retract and compress the spring  60 . Once the rods have retracted into their respective bellows cup  52 , they no longer engage the wafer  70 . Concurrently, with the retraction of the rods or pins  62 , the pad structure will contact the outer portions  57  of the bellows cups  52 , (see FIG. 3). This contact pushes the outer portions  57  inward. Due to its resilience and shape, the bellows cups  52  twist causing their inner portions  58  to move outward imparting to the wafer  70  a slight push in the direction of the polishing pad. This slight push frees the wafer  70  from the end effector  10  and with the suction from the pad, the polishing pad can grab hold of the wafer. The end effector  10  is then moved away from the pad, and the springs  60  push the rods or pins  62  back to their original positions.  
         [0024]    Upon completion of the polishing process the wafer  70  is returned to the end effector  10  as follows. The up side of the effector is brought to the polishing pad and has the slideable finger assembly  32  fully retracted. The wafer  70  is then released onto the surfaces  34 ,  44 . The slideable finger assembly  32  is then extended until the wafer  70  rests on the top surface of the inner portions  58  and is held by the rods or pins  62 . If a wafer is being held on the bottom side of the paddle, the end effector  10  can be rotated 180 degrees and the above mentioned processes repeated.  
         [0025]    By being able to carrying two wafers, the end effector  10  is more efficient that single wafer systems. Further, as the end effector  10  grips wafers on their edges, damage to the top and bottom surfaces of the wafers is avoided. Further, the twist effect of head portions assists in transferring the wafers to the device reducing the magnitude of the required suction, thus avoiding further damage to the wafers.  
         [0026]    Although the invention has been described in terms of a polishing pad process, it will be appreciated by those skilled in the art that the invention can be used in all sorts of other wafer processing steps. Accordingly, various changes and modifications may be made to the illustrative embodiment without departing from the spirit or scope of the invention. It is intended that the scope of the invention not be limited in any way to the illustrative embodiment shown and described but that the invention be limited only by the claims appended hereto.