Abstract:
A robotic arm assembly ( 101 ) is provided which comprises a hub ( 103 ), a first arm segment ( 105 ) which is attached to the hub, and a second arm segment ( 107 ) which is attached to the first arm segment such that said second arm segment can rotate at least partially about its longitudinal axis.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention pertains generally to robotic arms, and more particularly, to wrist assemblies for robotic arms of the type useful in wafer processing equipment.  
       BACKGROUND OF THE INVENTION  
       [0002]     Modern semiconductor processing systems include cluster tools that integrate a number of process chambers together in order to perform several sequential processing steps without removing the substrate from the highly controlled processing environment. These chambers may include, for example, degas chambers, substrate pre-conditioning chambers, cooldown chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers, and etch chambers. The combination of chambers in a cluster tool, as well as the operating conditions and parameters under which those chambers are run, are selected to fabricate specific structures using a specific process recipe and process flow.  
         [0003]     Once the cluster tool has been set up with a desired set of chambers and auxiliary equipment for performing certain process steps, the cluster tool will typically process a large number of substrates by continuously passing them, one by one, through a series of chambers or process steps. The process recipes and sequences will typically be programmed into a microprocessor controller that will direct, control and monitor the processing of each substrate through the cluster tool. Once an entire cassette of wafers has been successfully processed through the cluster tool, the cassette may be passed to yet another cluster tool or stand alone tool, such as a chemical mechanical polisher, for further processing.  
         [0004]     One example of a fabrication system of the type described above is the cluster tool disclosed in U.S. Pat. No. 6,222,337 (Kroeker et al.), and reproduced in  FIGS. 1 and 2  herein. The magnetically coupled robot disclosed therein is equipped with robotic arms having a frog-leg type construction that are adapted to provide both radial and rotational movement of the robot blade within a fixed plane. The radial and rotational movements can be coordinated or combined to allow for pickup, transfer and deliver of substrates from one location within the cluster tool to another location. For example, the robotic arm may be used to move substrates from one processing chamber to an adjacent chamber.  
         [0005]      FIG. 1  is a schematic diagram of the integrated cluster tool  10  of Kroeker et al. Substrates are introduced into, and withdrawn from, the cluster tool  10  through a cassette loadlock  12 . A robot  14  having a blade  17  is located within the cluster tool  10  to transfer the substrates from one process chamber to another. These process chambers include cassette loadlock  12 , degas wafer orientation chamber  20 , preclean chamber  24 , PVD TiN chamber  22  and cooldown chamber  26 . The robot blade  17  is illustrated in the retracted position in which it can rotate freely within the chamber  18 .  
         [0006]     A second robot  28  is located in transfer chamber  30  and is adapted to transfer substrates between various chambers, such as the cooldown chamber  26 , preclean chamber  24 , CVD Al chamber (not shown) and a PVD AlCu processing chamber (not shown). The specific configuration of chambers illustrated in  FIG. 1  is designed to provide an integrated processing system capable of both CVD and PVD processes in a single cluster tool. A microprocessor controller  29  is provided to control the fabricating process sequence, conditions within the cluster tool, and the operation of the robots  14 ,  28 .  
         [0007]      FIG. 2  is a schematic view of the magnetically coupled robot of  FIG. 1  shown in both the retracted and extended positions. The robot  14  (see  FIG. 1 ) includes a first strut  81  rigidly attached to a first magnet clamp  80  and a second strut  82  rigidly attached to a second magnet clamp  80 ′. A third strut  83  is attached by a pivot  84  to strut  81  and by a pivot  85  to a wafer blade  86 . A fourth strut  87  is attached by a pivot  88  to strut  82  and by a pivot  89  to wafer blade  86 . The structure of struts  81 - 83 ,  87  and pivots  84 ,  85 ,  88 , and  89  form a “frog leg” type connection of wafer blade  86  to magnet clamps  80 , 80 ′.  
         [0008]     When magnet clamps  80 , 80 ′ rotate in the same direction with the same angular velocity, then the robot also rotates about axis x in this same direction with the same velocity. When magnet clamps  80 ,  80 ′ rotate in opposite directions with the same absolute angular velocity, then there is no rotation of assembly  14 , but instead there is linear radial movement of wafer blade  86  to a position illustrated by dashed elements  81 ′- 89 ′.  
         [0009]     A wafer  35  is shown being loaded on wafer blade  86  to illustrate that the wafer blade can be extended through a wafer transfer slot  810  in a wall  811  of a chamber  32  to transfer such a wafer into or out of the chamber  32 . The mode in which both magnet clamps  80 ,  80 ′ rotate in the same direction at the same speed can be used to rotate the robot from a position suitable for wafer exchange with one of the adjacent chambers  12 ,  20 ,  22 ,  24 ,  26  (see  FIG. 1 ) to a position suitable for wafer exchange with another of these chambers. The mode in which both magnet clamps  80 ,  80 ′ rotate with the same speed in opposite directions is then used to extend the wafer blade into one of these chambers and then extract it from that chamber. Some other combination of clamp rotation can be used to extend or retract the wafer blade as the robot is being rotated about axis x.  
         [0010]     To keep wafer blade  86  directed radially away from the rotation axes x, an interlocking mechanism is used between the pivots or cams  85 ,  89  to assure an equal and opposite angular rotation of each pivot. The interlocking mechanism may take on many designs. One possible interlocking mechanism is a pair of intermeshed gears  92  and  93  formed on the pivots  85  and  89 . These gears are loosely meshed to minimize particulate generation by these gears. To eliminate play between these two gears because of this loose mesh, a weak spring  94  (see  FIG. 4 ) may be extended between a point  95  on one gear to a point  96  on the other gear such that the spring tension lightly rotates these two gears in opposite directions until light contact between these gears is produced.  
         [0011]     Although robots of the type depicted in U.S. Pat. No. 6,222,337 (Kroeker et al.) have many desirable features, robots of this type also have some shortcomings. In particular, it has been found that robots of this type often exhibit excessive wear in the wrist  85 ′,  89 ′ and elbow  84 ′,  88 ′ joints. This problem results in excessive maintenance requirements and interruptions to the manufacturing process. There is thus a need in the art for a robotic assembly which requires less maintenance and exhibits less wear in these areas. These and other needs are met by the devices and methodologies disclosed herein and hereinafter described.  
       SUMMARY OF THE INVENTION  
       [0012]     In one aspect, a robotic arm assembly is provided which comprises a hub, a first arm segment attached to the hub, and a second arm segment attached to the first arm segment (e.g., by way of a pin or other suitable means) such that the second arm segment can rotate at least partially about its longitudinal axis. The robotic arm assembly, which preferably has a frog-leg design, may further comprise a third arm segment which is pivotally connected to the second arm segment, an end effector (to which the third arm segment may be attached), a fourth arm segment attached to the hub, and a fifth arm segment attached to the fourth arm segment such that the fifth arm segment can rotate at least partially about its longitudinal axis. The robotic arm assembly may further comprise a sixth arm segment which is pivotally connected to the fifth arm segment and which is also connected to the end effector. Preferably, the third and sixth arm segments are attached to opposing sides of the end effector, preferably by way of wrist assemblies.  
         [0013]     In another aspect, a robotic arm assembly is provided which comprises a hub, a lower arm attached to said hub, a forearm pivotally attached to said lower arm, and an end effector attached to said forearm, wherein said lower arm comprises a first segment which is rotatably connected to a second segment.  
         [0014]     In still another aspect, a robotic arm assembly is provided herein which comprises a hub, a first arm segment attached to said hub, and a second arm segment attached to said first arm segment such that said second arm segment can move with respect to said first arm segment in such a way as to relieve stress on the arm.  
         [0015]     One skilled in the art will appreciate that the various aspects of the present disclosure may be used in various combinations and sub-combinations, and each of those combinations and sub-combinations is to be treated as if specifically set forth herein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:  
         [0017]      FIG. 1  is an illustration of a cluster tool equipped with a robotic wafer handling system;  
         [0018]      FIG. 2  is an illustration of the arm assembly of the robot depicted in  FIG. 1 , and illustrates the retracted and extended positions of the arm assembly;  
         [0019]      FIG. 3  is an illustration of the wrist assembly of the robot depicted in  FIG. 1 ;  
         [0020]      FIG. 4  is an illustration of a prior art robotic arm assembly and illustrates the retracted and extended positions of the arm assembly; and  
         [0021]      FIG. 5  is an illustration of one embodiment of a robotic arm made in accordance with the teachings herein. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     The aforementioned needs are met by the devices and methodologies disclosed herein. In particular, after careful investigation, it has now been found that, in conventional robotic arms of the type illustrated in  FIGS. 1-4 , the hub assembly can move out of concentricity with its piece parts and force the lower arm to roll away from the rotating hub axis. For example, in some known robotic arm configurations, the hub to which the arm is attached contains three concentric rings. The top and bottom rings in this configuration house bearings and are attached to the arm, and the middle ring houses one or more rare earth magnets for the magnetic coupling drive. In use, these rings can deviate from concentricity, thus causing the aforementioned roll.  
         [0023]     In a frog-leg construction such as that depicted in  FIGS. 1-4 , this roll is transferred along the beam of the lower arm such that the arm is now out of parallelism with the second half of the frog arm. This condition induces stress within the wrist, elbow and hub assemblies, causing premature wear and adding abnormal motions in the z-direction (the direction perpendicular to the plane in which the arms extend and retract) as the arm is in motion. The devices and methodologies disclosed herein provide a means for compensating for this roll, thus eliminating such premature wear and allowing the robotic arm to operate properly.  
         [0024]      FIG. 5  illustrates one non-limiting embodiment of the lower portion of a robotic arm made in accordance with the teachings herein. Some of the details of the robotic arm have been eliminated for simplicity of illustration. The robotic arm  101  comprises a hub  103 , a first segment  105  which is attached to one or more rotating rings or columns in the hub, and a second segment  107  which is attached to the first segment by way of a pin  109 .  
         [0025]     The first  105  and second  107  segments are fastened together with a set of bolts  111  which mate with a set of threaded apertures (not shown) provided in the second element  107 . The throughput for the bolts in the first segment is sufficiently larger than the bolt itself such that the first element can rotate slightly around the axis of the pin  109  when the bolt is sufficiently loosened and when the arm is subjected to roll. Preferably, this rotation is within the range of ±2° which, though small, is sufficient to relieve the stress that would otherwise be placed on the wrist and elbow assemblies. Hence, the two-part construction of the lower arm depicted in  FIG. 5  allows a rotation to occur to compensate for the out-of-axis roll and to keep the entire arm balanced.  
         [0026]     While  FIG. 5  illustrates one particular means by which roll (and the accompanying stress) may be compensated for, one skilled in the art will appreciate that this objective may be achieved through a number of different means. For example, the first and second segments in  FIG. 5  could be connected across a bearing assembly which permits limited rotation of these segments with respect to each other. It will thus be appreciated that these various means are within the scope of the present invention. Thus, although particular embodiments of the devices and methodologies disclosed herein have been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention.