Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     (Not applicable) 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to substrate handling systems, and more particularly, to systems using robots to transport substrates between different locations. 
     2. Description of Related Art 
     During integrated chip manufacture and other industrial applications, substrates such as semiconductor wafers undergo numerous processing steps. Typically, these steps take place in dedicated processing stations remotely situated from each other and from the storage containers or cassettes used to hold the substrates. In integrated chip manufacture, the semiconductor wafers from which the chips are fabricated need to be contained in a carefully controlled environment in which temperature, humidity, and contaminant level, among other factors, need to be carefully controlled. Robots are often deployed to transport the wafers between processing stations, or to retrieve and return the wafers to the storage cassettes before and after processing. 
     One prior art arrangement for handling semiconductor substrates is shown in FIG. 1, wherein a robot arm  10  is used to transport the substrates (not shown) between a bank of processing stations  12 . Robot arm  10  has three arm links  14 ,  16  and  18  mounted in a base  19 . Proximalmost link  14  is rotatably mounted at its proximal end to base  20 , and links  16  and  18  are similarly mounted such that each succeeding link is rotatably mounted to the distalmost end of the preceding link. Rotation of links  14 ,  16  and  18  is mechanically coupled, using suitable linkages such as belts and pulleys (not shown), such that the distal end of distalmost link  18  can be extended or retracted relative to base  20 . A first motor (not shown) motivates this motion. The distal end of distalmost link  18  supports an end effector  22  which may be mounted for independent motion, using a second motor (not shown), such that yaw motion of the end effector can be achieved. 
     To laterally extend the reach of robot arm  10 , base  20  is mounted for translation in the x direction, on a track  24 . In this manner, robot arm  10 , and end effector  22  in particular, can be moved along the x direction to reach an increased number of processing stations  12 . A third motor (not shown) is used to effect this translation. 
     The above prior art arrangement suffers from several disadvantages. First, valuable space is wasted by track  24  and the supporting components required to translate robot arm  10  in the x direction, space generally delineated by the dashed line  26  in FIG.  1 . Second, motion along track  24  generates friction, which in turn generates particles which contaminate the “clean room” environment required for semiconductor processing. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention addresses the aforementioned and other disadvantages of the prior art by providing a robot arm in which an end effector linkage is mounted on an extensible linkage. Extension or retraction of the extensible linkage causes translation of the end effector linkage in the X direction, thereby increasing the range of the robot arm in the X direction. The motions of the extensible linkage and the end effector linkage are decoupled, and motion of one linkage is independent of motion of the other linkage. 
     The extensible linkage can be used to support more than one end effector linkage. Each end effector linkage can be mounted for motion which is independent from the other end effector linkage(s) and from the extensible linkage. In this manner, more than one processing station or storage location can be accessed by the robot arm. 
     In accordance with the invention, a robot arm as described above is mounted on a robot housed within a micro-environment enclosure in which semiconductor processing is effected. Process and/or storage stations are in communication with micro-environment enclosure, with the robot serving to transport substrates therebetween. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
     Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
     FIG. 1 is a schematic top view of a prior art substrate handling system; 
     FIG. 2 is a schematic top plan view of a substrate handling system in accordance with the invention; 
     FIG. 3 is a schematic top view of a robot in accordance with the invention; 
     FIG. 4 is a schematic side elevational view of the robot of FIG. 3; 
     FIG. 5 is a schematic top view of a robot in accordance with the preferred embodiment of the invention; 
     FIG. 6 is a schematic partial side elevational view of the robot of FIG. 5; and 
     FIG. 7 is a schematic front elevational view of the robot of FIG. 5 with a substrate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 shows a robot  20  having a robot arm  30  in accordance with the invention. Robot  20  and robot arm  30  are contained within a micro-environment enclosure  32  which is in communication with a plurality of stations  34  arranged along two rows  36  and  38 . Each station  34  can be a processing station in which steps of a semiconductor manufacturing process are to be performed on a semiconductor wafer (not shown), or a storage module such as a cassette containing a stack of such wafers. 
     Robot arm  30  comprises an extensible linkage  40  and an end effector linkage  50 . Extensible linkage  40  comprises individual links  42 ,  44  and  46 , with link  42  being considered proximalmost and being rotatably mounted at a proximal portion thereof in robot  20 . Similarly, link  44  is rotatably mounted at a proximal portion thereof to a distal portion of link  42 , and link  46  is rotatably mounted at a proximal portion thereof to a distal portion of link  44 . It will be understood that the terms “proximal,” “proximalmost,” “distal,” and “distalmost,” used herein are relative terms and are not to intended to be limited to any specific physical elements described, but are rather intended to merely designate relationships between elements. 
     End effector linkage  50  is mounted at the distal portion of distalmost link  46  of extensible linkage  40 . An end effector support structure  58  is provided at the distal portion of link  46  for supporting the end effector linkage  50 . End effector linkage  50  comprises proximalmost link  52  mounted at a proximal portion thereof to support structure  58 . Link  52  is rotatable, either by virtue of rotation relative to structure  58  or by rotation of structure  58  itself. Rotation is imparted using a suitable motor discussed below. Link  54  is rotatably mounted at a proximal portion thereof to a distal portion of link  52 . At the distal portion of link  54 , an end effector  56  is rotatably mounted and suitably configured for holding substrates such as semiconductor wafers and conveying these to or from the different stations  34 . 
     Motion of linkages  40  and  50  is preferably decoupled. In this manner, extensible linkage  40  serves to generally transport end effector linkage  50  laterally along the X direction by translating distalmost portion of link  46 , to which end effector linkage  50  is mounted, along a lateral trajectory. End effector linkage  50  is thus transported to the vicinity of the desired station  34 , thereby enabling end effector linkage  50  to reach the station  34  in order to deliver the wafer thereto or retrieve it therefrom. Such motion of end effector linkage  50 , and of end effector  56  in particular, may be along a straight line trajectory or a different trajectory depending on the arrangement of stations and the particular application contemplated. Additionally, it will be appreciated that the motions of the linkages  40  and  50 , while decoupled mechanically, may be synchronized in time so as to reduce the length of time required to reach a particular station  34 . Specifically, extension or retraction of extensible linkage  40  may occur during a first duration, while extension or retraction of end effector linkage  50  may occur during a second duration. However, the first and second durations may at least partially overlap to reduce overall time of the combined motions. Of course, such synchronization would be governed by the particular layout of the system as a whole, taking in account the presence of obstacles at a particular instant during motion of the linkages  40  and  50  and the end effector  56 . 
     Motion to extensible linkage  40  is imparted using a first, R-axis motor  62  housed in robot  20  as shown in FIGS. 3 and 4. R-axis motion is the extension and retraction motion of linkage  40  along the X direction, with the origin of this radial motion being taken to be rotation axis  63  of the proximal portion of proximalmost link  42 . Rotation of motor  62  is transferred to links  42 ,  44  and  46  via a first mechanical linkage which includes belts  64  and  66  cooperating with pulleys such as pulley  68 , as seen from FIGS. 3 and 4. It will be appreciated that the number of links of the extensible linkage  40  and end effector linkage  50  can be different from that described. In the three-link arrangement, the mechanical linkages used to couple the links preferably provide a 1:2 motion ratio between the first and second link and then a 2:1 ratio between the second and third link so that the result is linear motion of the linkage as a whole. Accordingly, as mentioned above, rotation of motor  62  results in extension and retraction of linkage  40  in a straight line in the x direction, thereby translating end effector linkage  50  mounted thereon in the direction of rows  36  and  38  of stations  34 . Other motions, of course, are possible, depending on the particular application and the arrangement of stations  34  to be accessed. For instance, robot arm  30  can also be rotated (T-axis motion), for example to accommodate a different arrangement of stations  34 . T-axis motion can be provided by a motor  70  in robot  20 . In FIG. 4, the T-axis is shown to be coincident with axis  63  about which link  42  rotates. It will be appreciated that this is not necessary, however, and a non-coincident configuration is also contemplated. 
     End effector linkage  50  can be extended and retracted independently of extensible linkage  40 . Extension/retraction motion of end effector linkage  50  is motivated by motor  72  provided in support structure  58 . A suitable belt and pulley linkage, including belts  69  and  71  for instance, transfers rotation of motor  72  to links  52  and  54  and end effector  56  in a manner similar to that described with respect to extensible linkage  40 . The extension/retraction motion of end effector linkage  50  will be referred to as secondary radial motion as referenced from support structure  58 . Motors  62  and  72  corresponding to extensible linkage  40  and end effector linkage  50 , respectively, are independently actuated such that the motions of the two linkages are decoupled. 
     The arrangement of FIG. 1 is such that two rows ( 36 ,  38 ) of stations  34  are arranged in opposing relation, with arm  30  disposed therebetween. To access confronting stations, end effector  56  is mounted in end effector linkage  50  such that its motion is “reversible” and it can be “flipped” to access stations  34  from either row  36  or row  38 . Specifically, as seen from FIG. 3, links  52  and  54  and end effector  56  are stacked one on top of the other such that rotation of any of the links does not interfere with rotation of any other link. A similar arrangement is shown for the extensible linkage  40 , providing a “reversible” extension direction such that stations on either side of the robot  20  along the X direction can be accessed. In other words, the extensible linkage  40  can be made to extend either to the right or to the left of robot  20  in the plane of FIG.  1 . 
     End effector linkage  50  is also equipped for Y-axis, or yaw, motion. Such motion is provided by Y-axis motor  74  mounted to second link  44  of extensible linkage  40  and connected via belt  76  and pulleys  78  to support structure  58  in order to rotate the support structure and end effector linkage  50  mounted thereon. In this manner, Y-axis, or yaw, motion of end effector linkage  50  is achieved. This motion can be used to supplement or replace the secondary radial motion of end effector linkage  50  in order to achieve the reversible motion of the end effector  50  described above. Additionally, end effector  56  itself can be mounted to have yaw axis motion. A separate motor (not shown) can be provided for this purpose. 
     Robot  20  is preferably a GPR (Global Positioning Robot) type robot and is provided with elevational, Z-axis motion for arm  30 . A plurality of Z-axis motors  80  (only one is shown) mounted in a stationary frame  81  are used to vertically move a plate  82 , which is part of an elevatable frame in which arm  30  is mounted, in order to impart elevational motion to robot arm  30 . Robot  20  is also designed to be tiltable with respect to the Z axis in order to provide an additional degree of freedom to arm  30  generally and to end effector  56  in particular. Tilting is achieved by for example rotating motors  80  to different extents as described in detail in related U.S. Pat. Ser. Nos. 5,954,840 and 6,059,516 which are directed to a GPR robot and which are incorporated herein by reference. A GPR robot is a parallel-serial type manipulator, wherein the elevational, Z-axis motion comprises the parallel component and the substantially planar multiple link motion of arm  30  comprises the serial component. A parallel-serial manipulator is uniquely suited for use in the invention because it overcomes disadvantages associated with parallel manipulators and serial manipulators considered singularly. To achieve comparable degrees of freedom, serial manipulators require universal wrists and associated actuators, which are of significant size and weight but which cannot practically be placed close to the base of the robot in order to reduce the effect of their mass. On the other hand, parallel manipulators have very limited motion and working space. Exacerbating these constraints is the context of semiconductor processing, wherein severe limitations are imposed relating to manipulator weight and size and the type of components, such as motors, links, and mechanical linkages, used. These limitations are a function of the highly controlled conditions of friction, contamination, humidity, temperature, etc. GPR robots combine the advantages of parallel and serial manipulators, providing fast global (over a large working area) motion through simple planar (T, R, Y) serial arm and accurate elevational (Z) and tilting motion. 
     While described with respect to a single end effector  56  and end effector linkage  50 , in the preferred embodiment the robot arm is equipped with dual end effectors and associated linkages as shown in FIGS. 5-7. End effectors  92  and  94  are mounted in support structure  96  disposed at the distal portion of extensible linkage  98 , and more specifically, in distalmost link  99  thereof. Support structure  96  is rotatable such that Y-axis, or yaw motion, is achieved. A motor  100  and suitable mechanical linkage comprised of belt  102  and pulleys  104  motivate this motion, with motor  100  being mounted in second link  97  of extensible linkage  98 . End effector  92  is part of end effector linkage  106 , which includes links  108  and  110 . End effector  94  is part of end effector linkage  112 , which includes links  114  and  116 . Motors  118  and  120  motivate linkages  106  and  112 , respectively, using appropriate mechanical linkages which include belts  122  and  124  and pulleys  126  and  128 . Motion of linkages  112  and  116  is decoupled such that they can be moved independently of each other and of extensible linkage  98 . As seen from FIG. 7, end effectors  92  and  94  are designed to be offset vertically so that they can overlap when their respective linkages are extended to the same extent. To that end, upper end effector  92  is provided with a bracket portion  130  which is sized and shaped to clear any substrate, such as semiconductor wafer  132 , carried by lower end effector  94 . In this manner, end effectors  92  and  94  are capable of occupying the same radial and angular positions with respect to the mounting portion of the extensible linkage  40  in which end effector linkages  106  and  112  are mounted. 
     The use of two independently motivated end effectors  92  and  94  provides several advantages, including the ability to simultaneously access two oppositely disposed stations  34  from the dual-row arrangement of stations shown in FIG.  1 . Additionally, swapping of substrates from a single station  34  can be effected substantially simultaneously, with one end effector for example removing a substrate from a location within a station  34  and the other end effector substituting a second substrate into the same location. This obviates the need to remove the first substrate from the station  34 , drop off the first substrate at a different station  34 , pick up a second substrate, return to the first station  34 , and drop off the second substrate at the first station. The savings in time made possible by the dual end effector arrangement, which translate to substantial savings in processing costs, will be readily appreciated. 
     The above are exemplary modes of carrying out the invention and are not intended to be limiting. It will be apparent to those of ordinary skill in the art that modifications thereto can be made without departure from the spirit and scope of the invention as set forth in the following claims.

Technology Category: 7