Abstract:
A device for use in the semiconductor industry includes a robotic arm whose end effector includes at least two prongs designed to hold a substrate carrier. A pushing member located between the prongs can move independently of the prongs and is configured to exert force against the substrate carrier while the prongs are retracted from the substrate carrier, after the substrate carrier has been brought to its intended position. In this manner, the position of the substrate carrier is maintained at its intended position as the prongs are retracted. Each of the prongs may include a claw or gripping member for grasping the substrate carrier.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a robotic device, and more particularly, to an end effector suitable for transferring substrate carriers, such as those used in the semiconductor industry. 
       BACKGROUND 
       [0002]    A universal aspect of automated semiconductor processing systems (including advanced research deposition and analysis systems) is some form of transfer mechanism for moving substrates into, through, and out of process/deposition/analysis chambers. Since these systems are expensive, a reasonable return on investment necessitates high system through-put, which can be achieved only if the transfer mechanism is reliable. However, the demands of most processes create challenges to maintaining reliability of the transfer mechanism. These demands can include high or low temperatures, vacuum, corrosive gases, special material requirements, motion control requirements, special sensing requirements, or a combination of the foregoing. 
         [0003]    Transfer mechanisms, or robots, are generally designed to do a simple task, such as pick up a substrate carrier, move it, and place it in a desired location. Such simple actions are difficult in a vacuum—not just because of the obvious constraints of working in a vacuum, but also because of the significant effect that vacuum has on the tribological properties of materials. Unfortunately, the designs for robots to be used in vacuum are often derived from those designed for use in air, so that the reliability of robots in vacuum can degrade quickly. To mitigate reliability problems, several measures can be undertaken, such as avoiding contact or sliding between parts made of similar materials, using hard or wear-resistant coatings where contact does occur, and restricting movement to motions that are precise and carefully controlled to avoid collisions. Nevertheless, robotic devices having improved reliability and flexibility are desired. 
       SUMMARY 
       [0004]    This invention addresses one of the challenges associated with a robot placing its load at an intended position. In semiconductor processing equipment, an intended position can be a receiving mechanism, a platen, a chuck in a process chamber, or a slot in a cassette. In prior art devices, as the robot withdraws its end effector after releasing its load, any slight contact with the load can dislodge that load from its intended position. In this invention, the robot employs a mechanism, called a pusher, to ensure that the deposited load (e.g., the carrier and its substrate) remains in its intended position while the end effector is withdrawn. 
         [0005]    One aspect of the invention is a device that includes a robotic arm that has an end effector. The end effector includes i) at least two prongs designed to hold a substrate carrier and ii) a pushing member that can move independently of the prongs. The pushing member is configured to exert force against the substrate carrier while the prongs are retracted from the substrate carrier, thereby preventing the substrate carrier from being retracted while the prongs are retracted. The device further includes one or more motors for moving the pushing member and the prongs. 
         [0006]    A preferred method for use with this device includes the following steps: 
         [0007]    (a) bringing, by using the end effector, a selected substrate carrier to a desired position, the prongs holding the selected carrier while the selected carrier is being moved; 
         [0008]    (b) moving the pushing member towards the selected carrier, the pushing member exerting force against the selected carrier; 
         [0009]    (c) moving the prongs away from the selected carrier, while the pushing member continues to exert force against the selected carrier and thereby maintain the desired position of the selected carrier; and 
         [0010]    (d) retracting the pushing member so that it no longer contacts the selected carrier, 
         [0000]    in which steps (a), (b), (c), and (d) are carried out in turn (in that order). The method can be carried out under harsh conditions, e.g., at elevated temperatures, under vacuum, and/or in an oxidizing atmosphere such as that used in a deposition or etching process. 
         [0011]    Another aspect of the invention is a device that includes i) a forked member having ends that engage and hold a substrate carrier and ii) a pusher that extends between the ends of the forked member, so that the pusher can apply force against the substrate carrier as the forked member is retracted from the substrate carrier. 
         [0012]    Yet another aspect of the invention is a device that includes i) a plurality of extension members, the extension members having respective gripping members designed to hold a substrate carrier and ii) a pushing member between two of the extension members. The pushing member can be moved independently of each of the plurality of extension members; it is used for maintaining the position of a substrate carrier that has been brought to a desired position by exerting force against the positioned carrier when the extension members are retracted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates an embodiment of the invention housed within a robot chamber, which in turn is connected to one or more other chambers used for semiconductor processing. 
           [0014]      FIG. 2 , which includes  FIGS. 2A ,  2 B, and  2 C, show various views of a portion of a robotic device (that portion being designated herein as the “fork assembly”) and its end effector, including prongs for holding and moving a substrate carrier and a pusher for keeping the substrate carrier in place, in which: 
           [0015]      FIG. 2A  is a perspective view of the fork assembly; 
           [0016]      FIG. 2B  is a view of the underside of the fork assembly; and 
           [0017]      FIG. 2C  is a perspective view of the fork assembly with certain components related to the pusher removed from view, to better illustrate how the prongs and their claws function. 
           [0018]      FIG. 3  shows a substrate carrier at the distal end of the end effector. 
           [0019]      FIG. 4 , which includes  FIGS. 4A and 4B , illustrate views of the robotic device and its relationship to a rail along which it travels. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A preferred embodiment of the invention is now described with respect to the figures.  FIG. 1  shows a robotic device  110  mounted within a robot chamber  120  (shown as a cutaway for clarity). The robot chamber  120  includes a viewing port  130  that includes transparent glass through which the robotic device  110  can be viewed. The robotic device  110  can be moved through the robot chamber  120  towards an adjacent load lock chamber or cassette loading chamber (not shown, but the load lock chamber would be connected to, and to the right of, the robot chamber  120  in  FIG. 1 ), where a substrate carrier can be loaded or removed from the robotic device  110 . The load lock chamber is in turn connected to a process chamber (not shown, but still further to the right), such as a deposition chamber or an etching chamber, where materials may be deposited onto a substrate or wafer positioned by the robotic device  110 . Electrical power is supplied to the robotic device  110  through a ribbon cable  140  that passes through an electrical feedthrough  150 . More precisely, the portion of the ribbon cable  140  that is external to the robot chamber  120  mates with electrical pins (not shown) in the electrical feedthrough  150 , and the portion of the ribbon cable  140  within the robot chamber  120  likewise mates with the electrical pins, so that no mechanical feedthrough is used that might otherwise compromise the integrity of the vacuum. Alternatively, the cable  140  external to the robot chamber  120  need not be a ribbon cable. To the left of the robot chamber  120  is a distance sensing laser assembly  160 . A laser beam (not shown) directed through the glass of a second viewing port  170  can be used to establish the approximate position of the robotic device  110 . 
         [0021]      FIGS. 2A and 2B  show in greater detail that portion of the robotic device  110  designated as the fork assembly  200 , which includes a fork  205  with its two prongs  210  that house respective motor-actuated claws  215 . The fork assembly  200  also includes a pusher  220 . The end effector portion of the robotic device  110  can be used to manipulate a substrate carrier  225 . The claws  215  are retracted in  FIGS. 2A and 2B , but as is evident from  FIG. 3 , when the claws are extended they can be used to grasp and restrain the substrate carrier  225  so that it can be moved securely from one location to another. (A substrate can be placed in the center, hollow portion of the substrate carrier  225  and then overlaid with a block of SiC, which can be heated with infrared radiation to heat the underlying substrate; neither the substrate nor the SiC block is shown in  FIG. 3 .) 
         [0022]    Once the substrate carrier  225  has been brought to an intended position, it is released by bringing the claws  215  to their retracted position (see  FIGS. 2A and 2B , in which the claws are retracted). The prongs  210  are then pulled back from the substrate carrier  225 ; note that the prongs slide underneath flange portions  230  of the substrate carrier as they are retracted from the substrate carrier. Unfortunately, even slight contact between mechanical parts under vacuum can generate high frictional forces. Thus, one could imagine that as the prongs  210  are withdrawn, the substrate carrier  225  might be unintentionally dragged along as a result of accidental contact with the prongs, thereby dislodging the substrate carrier from its intended position. 
         [0023]    To circumvent this problem, when the claws  215  release the substrate carrier  225 , the pusher  220  moves towards the substrate carrier until contact occurs (or alternatively, the pusher may be brought into contact with the substrate carrier before or after the claws release the substrate carrier). The pusher  220  is used to apply force against the substrate carrier  225  while the prongs  210  are retracted, as shown in  FIGS. 2A and 2B ; doing so keeps the substrate carrier  225  in place (e.g., at a desired location in a process chamber or in a cassette in a load lock chamber). 
         [0024]    Actuation of the pusher  220  is now described with respect to  FIGS. 2A and 2B . A pusher motor  235  is mechanically tied to various components designated collectively as the pusher drive mechanism  240 . The pusher drive mechanism  240  may include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The pusher drive mechanism  240  engages a pusher drive rod  245 , thereby pushing this rod either forwards or backwards relative to the fork  205 . The pusher drive rod  245  is in turn fixed to a pusher guide block  250 , which in turn is connected to the pusher  220  (see  FIG. 2B , which shows the underside of the fork assembly  200 ). As the pusher guide block  250  is moved forwards or backwards within a groove in the fork  205 , the pusher  220  is likewise moved forwards or backwards. In this manner, the pusher  220  can be made to butt up against the substrate carrier  225  or retracted from it. Two pusher guide brackets  255  help keep the pusher  220  in place as it is moved back and forth. 
         [0025]    Actuation of the claws  215  is now described with respect to  FIGS. 2A and 2C . In  FIG. 2C  components related to operation of the claws  215  are visible, whereas for clarity certain components unique to operation of the pusher  220  have been removed from view. A claw motor  260  is mechanically tied to various components designated collectively as the claw drive mechanism  265 . The claw drive mechanism  265  may include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The claw drive mechanism  265  engages a claw drive rod  270 , thereby pushing this rod either forwards or backwards relative to the fork  205 . The claw drive rod  270  is in turn fixed to a claw guide block  275 , which is secured by two clamps  280 . The claw guide block  275  is in turn secured to a beam  285 , whose motion is constrained by guide members  287  located on both sides of the beam. 
         [0026]    When the beam  285  moves forwards, two links  290  rotate to allow the proximal ends of levers  294  to move in an outward direction, so that the claws  215  at the distal ends of the levers are deployed from out of their respective prongs  210  (as the levers rotate about respective pivots  296 ), thereby permitting the claws  215  to grasp a carrier  225 . Specifically, two springs  298  acting between the fork  205  (not shown in  FIG. 2C ) and respective levers  294  urge the two rotating links  290  (each having 3 arms) to maintain contact with pins  297  that are attached to the beam  285  and extend below the beam. (Each spring  298  fits within a notch in a respective lever  294  and a hole in the fork  205 ). 
         [0027]    Conversely, the claws  215  are retracted when the claw drive rod  270  is moved backward. Specifically, as the beam  285  is retracted, the pins  297  contact the rotating links  290 , causing them to rotate. This in turn causes the levers  294  to rotate inward, which compresses the springs  298 . Note that the rotating links  290  are constrained in one direction by respective adjustable stops  299 , so that the claws  215  do not extend too far inward when they are deployed; motion of the rotating links  290  is constrained in the other direction by a sensor in the claw drive mechanism  265 , so that the claws  215  do not rotate out of the prongs  210  when they are retracted. 
         [0028]    Movement of the fork assembly  200  is now described with respect to  FIGS. 4A and 4B .  FIG. 4A  shows the fork assembly  200  in combination with other components designed to permit the fork assembly to move back and forth throughout the robot chamber  120  (see also  FIG. 1 ). An exploded view of the same is shown in  FIG. 4B , which shows the fork assembly  200 , an upper carriage block  320 , a rail  325 , and a lower carriage block  330 . When these components are assembled, the fork assembly  200  can move along and over the rail  325 . 
         [0029]    The upper carriage block  320  includes two drive motors  335 , which when run together provide the torque necessary to drive the upper carriage block, the lower carriage block  330 , and the fork assembly  200  along a gear rack  338  of the rail  325 . The upper carriage block  320  includes two translational rollers  340   a  that run within a groove  345   a  in the rail  325 . A pin (not shown) extends between a pinhole  350  in the upper carriage block  320  and the fork assembly  200 , thereby holding together the upper carriage block and the fork assembly. 
         [0030]    The lower carriage block  330  includes a translational roller  340   b  and centering rollers  355 , all of which run along a groove  345   b  within the underside of the rail  325 . Pins and screws that fit within pin holes  360  and screw holes  365 , respectively, permit the lower carriage block  330  to be fixed precisely to the upper carriage block  320 . 
         [0031]    As mentioned previously, once the substrate carrier  225  has been brought to an intended location, the pusher  220  is used to apply force against the substrate carrier while the prongs  210  are retracted. Otherwise, the substrate carrier  225  might be unintentionally dislodged from its intended location (e.g., within a cassette in a load lock chamber or a deposition chamber). Preferably, the pusher  220  is in contact with the substrate carrier  225  for the entire time that the prongs  210  are being retracted. One way to accomplish this is to synchronize the motion of the fork assembly  200  (with its prongs  210 ) and the motion of the pusher  220 , so that the distal end of the pusher extends away from the end effector (located at the distal end of the fork assembly) at the same speed that the end effector is retracted from the substrate carrier  225 . To this end, the actions of the pusher motor  235  and the drive motors  335  may be coordinated using a motion controller (not shown) to control the respective movements of the pusher motor and drive motors, so that the fork assembly  200  retreats along the rail  325  at the same speed that the pusher  220  moves forward relative to the fork assembly. That is, the net effect is that the pusher  220  does not move with respect to the rail  325  (which is generally fixed) or the substrate carrier  225  (which is to be kept stationary at an intended location). Alternatively, the drive motors  335  may simply be turned off, and the pusher  220  (driven by the pusher motor  235 ) may push against the substrate carrier  225 , so that the fork assembly  200  and its prongs  210  (along with the upper carriage block  320  and the lower carriage block  330 ) are pushed away from the substrate carrier. 
         [0032]    The various parts of the robotic device  110  may be machined from stock materials. The fork  205  may be advantageously made of molybdenum, since it is thermally and mechanically stable. Alternatively, the fork  205  could be made from a ceramic material such as Macor® (although ceramics are more brittle), or the fork could be made out of more compliant materials, such as plastic (e.g., polyimide), if the substrate carrier were made of a relatively soft material. Other parts in the fork assembly  200 , such as the claws  215  and the pusher  220 , can be made of stainless steel, for example. The substrate carrier  225  is preferably fabricated from HAYNES® 230® alloy, which is designed to withstand oxidation (e.g., from oxygen or air) even at high temperatures (e.g., at 100° C., 150° C., 200° C., or greater), which are conditions encountered by the robotic device  110  described herein. At such high temperatures and under vacuum, oil-based lubricants are not recommended; rather, solid lubricants such as MoS 2  or WS 2  (e.g., Dicronite® coating) may be applied to parts such as gear surfaces to reduce friction. 
         [0033]    The dimensions of the various parts disclosed herein may be selected in view of the intended application. A robotic device  110  designed for use in a research environment (e.g., for transferring small wafers having a diameter of 20-30 mm) would be smaller than one designed for use in a manufacturing setting (e.g., for transferring wafers having a diameter of 300 mm). A smaller, research-oriented device may have, for example: prongs  210  having a length between 20 and 60-100 mm and a width between 6 and 12 mm; a fork assembly  200  whose range of motion is between 200 mm and 600 mm; a substrate carrier having a width and a length of 40-60 mm; and claws  215  whose hooked portion (the portion that contacts the substrate carrier) has a length of 1-3 mm. A larger device designed for manufacturing applications may have, for example: prongs  210  having a length between 300 and 350 mm and a width between 25 and 40 mm; a fork assembly  200  whose range of motion is between 600 mm and 1000 mm; a substrate carrier having a width and a length of 300-350 mm; and claws  215  whose hooked portion (the portion that contacts the substrate carrier) has a length of 2-6 mm. In either case, the range of motion of the pusher  220  is preferably comparable to that of the length of the prongs  210 . 
         [0034]    The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than the foregoing description. All changes within the meaning and range of equivalency of the claims are to be embraced within that scope.