Abstract:
A coaxial drive employs a base member which is secured to a housing and is open to atmosphere and mounts rotatably an interior drive shaft about said base member so that rotation of the drive member in either direction in a full 360° circle. An electrical slip ring is provided between the base and the drive member with a ferrofluidic seal disposed proximate the lower end of the interior drive shaft such that atmospheric pressure passing through the base member and through the electrical slip ring is blocked by the ferrofluidic seal which has an opposite end disposed to the vacuum in the central processing apparatus.

Description:
TECHNICAL FIELD 
     The apparatus of the present invention relates generally to material transfer devices. The material transferred might include, but not be limited to, semiconductor wafers, such as Silicon, Gallium Arsenide, semi conductor packing substrates, such as, High Density Interconnects, semiconductor manufacturing process imaging plates, such as masks or recticles, and large area display panels, such as Active Matrix LCD substrates. 
     The invention further relates to vacuum robot drive technologies for handling wafers or flat panels and relates more particularly to improvements in such technologies whereby electrical power can be brought to the robot arm for purposes of, wafer sensing, wafer gripping and or other sensory applications while nevertheless allowing robot arm angular movement to achieve unlimited rotation through 360 degrees. 
     Current vacuum robot drive technology for handling wafers or flat panels does not allow electrical power to be brought to the robot arm while simultaneously allowing for unlimited rotation of the drive joint. Providing continuous theta axis rotation to the rotating drive arms in a robot as set forth above to provide unlimited rotational drive, except for example, as limited by the geometry of the robot arms themselves, has been a long felt need. It has always been conceived that if electrical power could be brought from the robot drive to the robot arm, sensing, clamping or measurement devices could be added to the arm linkage. 
     However, one concern of the electrical feed through was that it would limit the rotation of the arm. If a limit on shaft rotation was placed in such a robotic device, the advantage of the added devices, e.g. sensing, clamping and measuring, would decrease the present capabilities of the device and make them less appealing in the market place. 
     Accordingly, it is an object of the present invention to provide an unlimited rotation robot drive which allows electrical power to be brought from outside the atmosphere side of the drive unit and into the arms which reside in a vacuum environment. 
     It is further object of the invention to provide an unlimited angular movement robot drive capable of unlimited angular rotation for the purpose of providing electrostatic wafer clamping, wafer sensing, arm positioning measurement, arm acceleration measurement and wafer position measurement. 
     It is still a further object of the invention to provide a system which enables unlimited angular rotations of the coaxial drive vacuum robot which is capable of being modified existing coaxial drive structures. 
     Further objects and advantages of the invention will become apparent from the following disclosure independent claims. 
     SUMMARY OF THE INVENTION 
     The invention resides in a coaxial for use in wafer handling and relates more specifically to an improvement therefor whereby the drive is capable of angular rotations fully in a 360 degree circle without interference from electrical connections. 
     More specifically, the invention resides in a coaxial drive having one part exposed to atmosphere and another part exposed to vacuum. The drive comprises a base member secured to a housing extending vertically therefrom along a central axis, and a drive member having a generally hollow internal confine is disposed over the base member for rotation in either rotational direction with a gap extending therebetween. The drive member and the base include a circumferentially disposed contact means concentrically located about the central axis and the base and the drive members having a contact leads which are located coincidentally with the contact means and in contact therewith along 360° relative rotation between the base member and the drive member. A seal is carried by the drive member and is located thereon between the atmosphere and the vacuum environments and prevents atmosphere from entering the vacuum environment. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the invention are explained in the following description taken in connection with the accompanying drawings, wherein 
     FIG. 1 is a schematic top plan view of a substrate processing apparatus having a substrate transport incorporating features of the present invention; 
     FIG. 1 a  is a perspective view of the same substrate transport drive assembly used in the apparatus used in FIG. 1; 
     FIG. 2 is a perspective view of the rotational drive assembly shown in FIG. 1 a.    
     FIG. 3 is a vertical sectional view of the drive assembly taken along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a schematic isolated view of the inner coaxial shaft of the feed through part of the drive assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown in a schematic top view of a substrate processing apparatus  10 . The apparatus  10  includes a substrate transport  12 , substrate processing modular  14  and load lock  16 . A similar substrate processing apparatus is disclosed in U.S. Pat. No. 4,715,921 which is hereby incorporated by reference in its entirety. U.S. patent application Ser. No. 08/048,833 discloses an articulated arm transfer device which is also hereby incorporated by reference in its entirety. The apparatus  10  is adapted to process substrates, such as, semiconductor wafers or flat panel displays, as is known in the art. 
     The transport  12  includes a housing  18 , a moveable arm assembly  20  and a drive assembly  22 . The processing modules  14  and load locks  16  are attached to sides of the housing  18 . The housing  18  forms a vacuum chamber in which the arm assembly  20  can transport substrates between and or among the load lock  16  and the processing modules  14 . The arm assembly  20  can be similar to that described in U.S. patent application Ser. No. 08/048,833 with substrates supporting and effectors  24 . In alternative embodiments, other types of housings and/or moveable arm assemblies could be used in conjuction with the present invention. 
     Referring now to FIG. 1 a , the drive assembly  22  is shown. The drive assembly  22  includes a frame  26 , a rotational drive assembly  28 , a vertical drive  30 , and a controller  32 . The drive assembly  22  is mounted to the underside U of the housing  18 . The frame  26  includes a top flange  34  which is stationarily attached to the mounting flange  35  which is secured to the bottom U of the housing  18 . A carriage driveably connected to the vertical drive  30  and disposed along ways on the frame  26  is controllably vertically moveably positionable between upper and lower positions as required by use. A top flange  34  as seen in FIG. 1 a  has a circular opening  48  and a portion of the drive shaft assembly of the rotational drive assembly  28  projects through the hole  48  and through a hole through the bottom U of the housing  18  into the vacuum chamber formed by the housing. A bellows  50  is provided between the underside U of the housing  18  and the drive assembly  28  to maintain the vacuum in the vacuum chamber, but allows the rotational drive assembly  28  to be moveable vertically relative to the housing  18 . 
     Referring now to FIG. 2, and the rotational drive assembly  28 . The rotational drive assembly  28  includes two rotational drive units  74  and  76 . A positioning signaling device  82  may be provided thereon for determining the real time position of the robot arms. The two units  74  and  76  are substantially identically identical to one another and are attached to one another in reverse orientation in a stacked vertical arrangement. Each unit  74 ,  76  has a housing  88  which are suitably sized and shaped to be located within the cage frame  26 . The units  74  and  76  are fixedly connected to each other to form a modular unit that is secured to the carriage of the drive assembly  22  driven by the vertical drive  30 . Each unit  74 ,  76  is adapted to independently angularly rotate one of two drive shafts  92 ,  94  of the driveshaft assembly  90 . The two driveshafts, outer and inner,  92  and  94 , are coaxially mounted to the rotational drive assembly  28  coincidentally about the central axis CA, and the top ends of the shafts  92  and  94  are each connected to a member of the moveable arm assembly  20  such that rotation of the driveshafts in a given angular direction causes a robot arms to rotate together, while rotation of the shafts  92 ,  94  in opposite directions causes the extension/retraction of the arms in a frog leg type manner. 
     Referring now to FIG. 3, it should be seen that the drive assembly shown therein are coaxially disposed along the central access CA of FIG. 4 within the drive units of  74 , 76  respectively. The radially outwardly disposed outer driveshaft  94  has an annular flange  100  disposed thereabout and has a set of permanent magnets  201  attached to the flange  100  and placed in juxtaposition relative to circumferentially surrounding coils (not shown) within the unit  74 . Likewise, the radially inwardly located inner driveshaft  92  connects through a plurality of axially extending bolts placed through openings  102 , which threadily engage with a lower inner coaxial shaft  104  such that both the lower inner coaxial shaft  104  and the inner driveshaft  92  are nonrotatably connected with one another in axial confrontation about the central access CA. 
     Adjacent the bottom end of the lower inner coaxial shaft  104  is a second annularly extending flange  106  on which is disposed a set of permanent magnets  202  which are in juxtaposition with coils (not shown) mounted to the lower housing  76  for the purpose of controllably rotating the inner driveshaft  92  between angular orientations. The lower inner axial shaft  104  and the outer coaxial driveshaft  94  are axially separated from one another by a separating flange  110  disposed therebetween, and as between the outer coaxial driveshaft  94  and the separating flange  110  with a bearing plate  112  interposed therebetween. 
     In accordance with the invention, it should be seen that a bottom plate  114  is provided at the bottom of the unit  76 . The bottom plate  114  has an opening or hole  118  which is exposed to atmosphere and is disposed coincidentally with the central axis CA. The isolation cup  120  is fixedly mounted to the bottom plate  114  about the hole  118  with an  0 -ring seal  122  therebetween. The isolation cup  120  is secured against movement to the bottom plate  114  through the intermediary of a plurality of connecting screws and locating pins  123 ,  123 . Rotatably disposed coaxially about the isolation cup  120  is the lower inner shaft  104 . The units  74  and  76  support the component parts shown in FIG. 3 in such a way, using suitable bearing means, that a vertically extending annular gap  140  is provided between the isolation cup  120  and the lower inner axial shaft  104 . 
     The isolation cup  120  has a hollow inner chamber  124  which extends coaxially about the central axis CA through between the upper and lower ends  124 U,  124 L thereof. The isolation cup  120  narrows towards its top end to define a generally cylindrical tubular collar portion  126 . Within the tubular collar portion  126  is located an electrical connector  125 . The electrical connector  125  is of a tubular shape and has a base  113  in which is formed an opening  119  through which wires  111  are passed which ultimately electrically connect to the robot arm. The connector  125  is secured by bolts  117  to the cup  120  in the manner illustrated. 
     Also disposed within the hollow tubular confines of the tubular collar portion  126  is a central contact shaft  130  which is nonrotatably and sealingly connected to the isolation cup  120  through the intermediary of a spline connection or a transverse fastening pin and seals. At bottom end of the central contact shaft  130  is disposed an electrical connector  128  which is configured to axially mate with the connector part  125 . The electrical connector  128  is secured against axial movement, such as by an annular groove and snap ring, to the shaft  130 . Since the electrical connector  128  is secured within an atmospheric environment which is allowed to pass through and beyond the connector  128 , the connection can be made using any suitable type of connection, such as by the snap-fit, or adhesive connection because the forces acting upon the connector will not be exaggerated, such as found in the case where atmosphere and vacuum interface exists. Thus, the shaft  130  is axially and rotatably immovable relative to the isolation cup  120 , and the frame of the assembly thereby preventing twisting of the electrical wires  111  which are fed upwardly through the hollow portion  132  of the shaft  130 . In this way, the feed through connection  125 / 128  and its associated wires can be removeable without disassembly of the robotic drive mechanism. Thus, the wires  111  connect to the connector  128  by the mating of the connector  125  inserted therewithin. 
     As illustrated in FIG. 4 the interiorly disposed driveshaft  92  has a coaxially disposed stepped opening  136  formed therein. The top end of the interiorly disposed driveshaft  92  has a seal cap  133  which provides an end wall and locks the opening  136  from vacuum. The stepped opening seal  136  is defined by a first cylindrical portion  135  having a diameter D 1  and a second cylindrical portion  137  having a diameter D 2  which is less than that of the first portion  135 . The first cylindrical portion  135  is correspondingly sized and shaped to receive a ferrofludic seal  139  which is disposed circumferentially and axially secured against movement about the central contact shaft  130 . The interior surface of the inner coaxial shaft  92  defining the second cylindrical portion  137  is correspondingly sized and shaped to receive for relative rotation therewith the upper end portion  130 U of the central contact shaft  130 . 
     As previously mentioned, the outer surface of the isolation cup  120  and the inner surface of the lower inner shaft  104  are spaced apart by the gap  140  which exposes the lower end  141  of the seal  136  to the vacuum within the chamber of the handling apparatus. Thus, as illustrated by the arrow line in FIG. 4, vacuum is presented against the end  141  of the seal  139  while the upper inner end  143  of the seal  139  is exposed to atmosphere thereby providing the required differential in pressure necessary for effecting proper functioning of the ferrofluidic seal  139 . It should be understood that the ferrofluidic seal  139  is one that is readily commercially available and sold for example by Ferrofluidics, Inc., of Naushua, N.H. and is known in the industry. 
     Referring now in greater detail to FIGS. 3 and 4, and to the means  151  for rotatatably maintaining an electrical connection between the top end of the shaft  130  and the inner coaxial shaft  92 , it should be seen that this means is comprised of a plurality of slip-rings and include a plurality of vertically spaced circumferentially disposed grooves  142   a-h  formed in the inner cylindrical surface of the second cylindrical portion  137  of the opening  136 . Each groove extends radially outwardly into the surface of the cylindrical opening portion  137  of the inner coaxial shaft  92 . Within each of these grooves is located an annular metallic contact  175  electrically connected and secured to the central contact shaft  130 . At the top end of the central contact shaft  130  and in the confronting surface of the inner surface of the cylindrical portion  137  of the interior drive shaft  92  is located a plurality of transversely extending openings  150   a - 150   h  (see FIG. 4) each located in alignment with an associated one of the contact grooves  142   a-h . Within each of the transverse openings  150   a - 150   h  is located a lead (not shown) corresponding and connected to one of the contact brushes  175  which are fixed to the shaft  130 . Each lead is further connected to a corresponding lead on the connector  128 . In the case of the drive member  92 , each of the contact brushes  175  corresponds to an electrical device in the robot arm. The grooves  142   a-h  in the surface  137  connect to the robot arm by lines within a conduit  171  (see FIG. 4) in the shaft  92  which communicate with a chamber  200  in the member  92 . The brushes  175  of the central contact shaft  130  maintain sliding point contact with the associated one of the annular metallic contact grooves  142   a-h  while those of the other part may have a fixed connection therewith. Electrical contact is thus maintained in a full  360  degrees circle by the sliding contact of the leads with the contact rings. 
     By the foregoing an improved coaxial drive electric contact has been described by way of the preferred embodiment. However, numerous modifications and substitutions may be had without departing from the spirit of the invention. For example, it is well within the purview of the invention to provide contact rings about the outer surface of the central shaft  130  such that pint contact is effected by the leads of either or both the inner coaxial shaft  982  and/or the central. 
     Accordingly the invention has been described by way of illustration rather than limitation.