Abstract:
A device for use in the semiconductor industry includes a robotic arm whose end effector includes electromagnetic means to hold a substrate carrier. A pushing member can move independently of a flat, spatula-like portion of the device and is configured to exert force against the substrate carrier while the spatula-like portion is 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 spatula-like portion is retracted.

Description:
TECHNICAL FIELD 
     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 
     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. 
     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 
     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. 
     An embodiment of the invention is a device that comprises a robotic arm that includes an end effector. The end effector has (i) an electrical and/or magnetic unit (e.g., the unit may be constructed so that both electrical and magnetic modes of operation are possible) that has on and off modes, such that this unit, when it is in the on mode, provides an attractive holding force between the unit and a substrate carrier (so that the position of the substrate carrier remains fixed) and (ii) a pushing member that is configured to exert force against the substrate carrier, thereby preventing the substrate carrier from being retracted while the unit is retracted. The device further includes a motor for moving the pushing member. 
     One embodiment of the invention is a device that comprises a robotic arm that includes an end effector. The end effector includes (i) a spatula member whose distal end includes an electrical and/or magnetic unit having on and off modes, such that this unit, when it is in the on mode, provides an attractive holding force between the unit and a substrate carrier (so that the position of the substrate carrier remains fixed) and (ii) a pushing member that is configured to exert force against the substrate carrier, thereby preventing the substrate carrier from being retracted while the unit is retracted. 
     The following exemplary method can be used in conjunction with the embodiments described herein. This method includes: 
     (a) using the end effector to bring a selected substrate carrier to a desired position, with the attractive force holding the unit and the selected carrier together while the selected carrier is moved; 
     (b) moving the pushing member towards the selected carrier, so that the pushing member exerts force against the selected carrier; 
     (c) moving the unit away from the selected carrier, while the pushing member exerts force against the selected carrier, thereby maintaining the desired position of the selected carrier; and 
     (d) retracting the pushing member so that the pushing member no longer contacts the selected carrier. 
     Steps (a), (b), (c), and (d) are preferably carried out in that order. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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. 
         FIG. 2 , which includes  FIGS. 2A ,  2 B, and  2 C, shows various views of a portion of a first embodiment of a robotic device (that portion being designated herein as the “assembly”) and its end effector, including both an electromagnetic unit (also shown in  FIG. 1 ) for holding and moving a substrate carrier, as well as a pusher for keeping the substrate carrier in place, in which: 
         FIG. 2A  is a perspective view of the assembly and the substrate carrier; 
         FIG. 2B  is a top cutaway view of the end effector and the substrate carrier; and 
         FIG. 2C  is a cutaway view of the coils in the electromagnetic unit. 
         FIG. 3 , which includes  FIGS. 3A ,  3 B,  3 C,  3 D, and  3 E, shows various views of a portion of a second embodiment of an assembly and its end effector, including both a magnetic unit for holding and moving a substrate carrier, as well as a pusher for keeping the substrate carrier in place, in which: 
         FIG. 3A  is a perspective view of the assembly and the substrate carrier; 
         FIG. 3B  is a top cutaway view of the end effector and the substrate carrier; 
         FIG. 3C  is a cross sectional view of the end effector and the substrate carrier; 
         FIG. 3D  is a view of the end effector and the substrate carrier, showing the magnetic unit in the “on” position; and 
         FIG. 3E  is a view of the end effector and the substrate carrier, showing the magnetic unit in the “off” position. 
         FIG. 4  is a perspective view of the end effector of a third embodiment, including both an electrostatic unit for holding and moving a substrate carrier, as well as a pusher for keeping the substrate carrier in place. 
         FIG. 5 , which includes  FIGS. 5A and 5B , illustrates views of one of the robotic devices and its relationship to a rail along which it travels. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments of the invention are 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 onto the robotic device  110  or, alternatively, removed from it and inserted into a receiver in the load lock chamber. 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 (or etched away from) 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 . 
     Electromagnetic Embodiment 
       FIG. 2A  shows in greater detail that portion of the robotic device  110  designated as the assembly  200 , which includes a spatula  205  having an electromagnetic unit  215  at its distal end. The assembly  200  also includes a pusher  220 . The end effector portion of the robotic device  110  can help position a substrate carrier  225  using the electromagnetic unit  215 , which includes at least one electromagnetic coil  217 . (Four such coils  217  are shown in  FIG. 2A .) When they are activated, the coils  217  hold the substrate carrier  225  as a result of the magnetic force between the coils and the substrate carrier, thereby permitting the substrate carrier  225  to be moved securely from one location to another. For the substrate carrier  225  (and the other substrate carriers described herein), a substrate can be placed in the center, hollow portion of the substrate carrier 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. 2A ,  2 B, or  2 C. 
     The substrate carrier  225  can then be brought to an intended position, e.g., the grooves  228  in the substrate carrier can mate with a receiver in a load lock chamber. At this point, the coils  217  can be deactivated by turning off the current supplied to them. The spatula  205  is then pulled back from the substrate carrier  225 ; note that the spatula slides underneath the substrate carrier as it is retracted from the substrate carrier. (This is most easily visualized with respect to  FIG. 2B , which shows the spatula  205  underneath, and in contact with, the substrate carrier  225 .) Unfortunately, even slight contact between mechanical parts under vacuum can generate high frictional forces. Thus, one could imagine that as the spatula  205  is withdrawn, the substrate carrier  225  might be unintentionally dragged along as a result of contact with the spatula, thereby dislodging the substrate carrier from its intended position. 
     To circumvent this problem, as the coils  217  are being deactivated, the pusher  220  is moved towards the substrate carrier until contact occurs (or alternatively, the pusher may be brought into contact with the substrate carrier before or after the coils are deactivated). The pusher  220  is used to apply force against the substrate carrier  225  while the spatula  205  is 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). 
     Actuation of the pusher  220  is now described with respect to  FIG. 2A . 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 spatula  205 . The pusher drive rod  245  is in turn fixed to a pusher guide block  250  (e.g., by a screw  252 ), which in turn is connected to the pusher  220  (e.g., by screws  253 ). As the pusher guide block  250  is moved forwards or backwards within a groove  251  in the spatula  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. 
     The coils  217  and their actuation are now described with respect to  FIGS. 2B and 2C .  FIG. 2B  shows two coils  217 , with two other coils being hidden underneath the substrate carrier  225 . Electrical current flows through the coils  217  so that the coils act as magnets; the two coils shown in  FIG. 2B  are magnets whose top ends have opposite polarities, e.g., north and south. The two other coils (which are not visible in  FIG. 2B ) have polarities such that coils that are at diagonals to each other have the same polarity. When the coils  217  are activated, magnetic flux lines from the electromagnets pass through the substrate carrier  225 , and the magnetic force keeps the substrate carrier in contact with the spatula  205 . The substrate carrier in this embodiment is made of magnetic material, such as martensitic stainless steel. Current may be supplied to the coils  217  through one or more wires  257 . The wiring to the coils  217  may be either in parallel or series, provided that the desired polarities are produced. 
     The construction of an individual coil  217  is illustrated in  FIG. 2C . The wires forming the coil  217  may be 23 gauge copper wire insulated with, for example, GE varnish that forms a sheath around the wire. The wire  257  may be wound around a bobbin  258  that surrounds a pole piece  259 . The pole pieces  259  may be made from material such as soft iron or silicon iron. 
     Shunted Magnet Embodiments 
       FIG. 3  shows another embodiment in which magnetic force is used to hold a substrate carrier.  FIG. 3A  shows in greater detail that portion of a robotic device (similar to the robotic device  110 ) designated as the assembly  200   a , which includes a spatula  205   a  having a magnet unit  218  at its distal end. The assembly  200   a  also includes a pusher  220   a . The end effector of this embodiment can help position a substrate carrier  225   a  using the magnet unit  218 , which is activated mechanically as described below. When the magnet unit  218  is activated, the substrate carrier  225   a  is held as a result of the magnetic force between a magnet  262  (shown in  FIG. 3C ) in the unit  218  and the substrate carrier, thereby permitting the substrate carrier  225   a  to be moved securely from one location to another. 
     The substrate carrier  225   a  can then be brought to an intended position, e.g., the grooves  228   a  in the substrate carrier can mate with a receiver in a load lock chamber. At this point, the magnet unit  218  can be deactivated. The spatula  205   a  is then pulled back from the substrate carrier  225   a ; note that the spatula slides underneath the substrate carrier as it is retracted from the substrate carrier. (This is most easily visualized with respect to  FIG. 3B , which shows the spatula  205   a  underneath, and in contact with, the substrate carrier  225   a .) 
     As with the previously described embodiment, to reduce the risk of dislodging the substrate carrier  225   a  from its intended position as the spatula  205   a  is withdrawn, the pusher  220   a  is moved towards the substrate carrier until contact occurs (e.g., the pusher may be brought into contact with the substrate carrier before, during, or after deactivation of the magnet unit  218 ). The pusher  220   a  is used to apply force against the substrate carrier  225   a  while the spatula  205   a  is retracted (see  FIGS. 3A and 3B ); doing so keeps the substrate carrier  225   a  in place (e.g., at a desired location in a process chamber or in a cassette in a load lock chamber). 
     Actuation of the pusher  220   a  is now described with respect to  FIG. 3A . A pusher motor  235   a  is mechanically tied to various components designated collectively as the pusher drive mechanism  240   a . The pusher drive mechanism  240   a  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   a  engages a pusher drive rod  245   a , thereby pushing this rod either forwards or backwards relative to the spatula  205   a . The pusher drive rod  245   a  is in turn fixed to a pusher guide block  250   a  (e.g., by one or more screws  252   a ), which in turn is connected to the pusher  220   a  (e.g., by one or more screws  253   a ). As the pusher guide block  250   a  is moved forwards or backwards within a slot  251   a  in the spatula  205   a , the pusher  220   a  is likewise moved forwards or backwards. In this manner, the pusher  220   a  can be made to butt up against the substrate carrier  225   a  or retracted from it. Two pusher guide brackets  255   a  help keep the pusher  220   a  in place as it is moved back and forth. 
     The magnet unit  218  and the movement of its magnet mount  261  and magnet  262  are now described. As seen in  FIGS. 3C and 3D , when the magnet unit  218  is activated or in the “on” position, the magnet  262  (which can be made of Nd 2 Fe 14 B, for example, and can be epoxied or otherwise secured to the magnet mount  261 ), is positioned between two pole pieces  263  (e.g., made of soft iron) and directly underneath the substrate carrier  225   a  (which is likewise made of a magnetic material). The magnetic attractive force between the magnet  262  and the substrate carrier  225   a  is sufficiently strong to hold the substrate carrier in place. This “on” position occurs when the magnet mount  261  (and the magnet  262  to which it is attached) is extended distally. As shown in  FIG. 3E , on the other hand, when the magnet mount  261  is retracted, the magnet  262  is partially surrounded by a shunt  264  and is far enough away from the substrate carrier  225   a  that there is no significant attractive force between the magnet and the substrate carrier; in this case, the magnet unit  218  is in the “off” position. Thus, the magnet mount  261  can be retracted or extended (as suggested by the double arrowhead in  FIG. 3B ), leading to the magnet unit  218  being deactivated or activated, respectively. 
     The magnet mount  261  can be extended or retracted with a magnet mount motor  260  as follows. The magnet mount motor  260  is mechanically tied to various components designated collectively as the magnet mount motor mechanism  265 . The motor mechanism  265  may include conventional components, such as one or more gears, lead screws, traveling nuts, and limit switches for constraining motion. The motor mechanism  265  engages a magnet mount drive rod  270 , thereby pushing this rod either forwards or backwards relative to the spatula  205   a . The drive rod  270  is in turn fixed to a magnet mount guide block  275  by one or more screws  281 . As the drive rod  270  is moved forwards or backwards, the magnet mount guide block  275  moves within the slot  251   a  in the spatula  205   a . The magnet mount  261  is likewise moved forwards or backwards, since the drive rod  270  is tied to the guide block  275 , and the guide block  275  is in turn tied to a magnet mount connector  285  that extends along the underside of the spatula  205   a  and is fixed to the magnet mount  261  (see  FIGS. 3D and 3E ). Limits switches in the pusher drive mechanism  240   a  and the magnet mount motor mechanism  265  ensure that the pusher guide block  250   a  and the magnet mount guide block  275  do not run into each other. 
     Other shunted magnet embodiments, which are not shown, are also contemplated. For example, the spatula may be embedded with one or more permanent magnets surrounded by a retractable sleeve made of mu-metal. When the sleeve surrounds the magnet(s), the magnetic field is effectively screened from the substrate carrier, so that it can be easily moved. On the other hand, when the sleeve is retracted, the magnetic field is able to interact with the substrate carrier, thereby fixing its location. In yet another shunted magnet embodiment, blocks of magnetic material separated by a block of non-magnetic material may be constructed so that the magnet can be turned on and off, in analogy with how magnetic bases are constructed (e.g., those used on optical tables). 
     Electrostatic Embodiment 
     In the embodiment shown in  FIG. 4 , electrostatic force is used to hold a substrate carrier. This embodiment is essentially identical to the electromagnetic embodiment described above in connection with  FIG. 2 , except at its distal end. An assembly  200   b  includes a spatula  205   b  having an electrostatic plate  219  (e.g., made of copper encapsulated with an insulator); alternatively, multiple electrodes may be embedded in the spatula. The assembly  200   b  also includes a pusher  220   b . The end effector portion of this embodiment can help position a substrate carrier  225   b  (which may include a dielectric plate or coating  290 ). When high voltage is applied to the electrostatic plate  219  (e.g., through a wire  292  that is tied to a voltage supply at the proximal end of the robotic device), an electrostatic force arises between the electrostatic plate  219  and the substrate carrier  225   b  due to redistribution of charge within that portion of the substrate carrier closest to the spatula  205 . The substrate carrier  225   b  is held in place as a result of this force, thereby permitting it to be moved securely from one location to another, like the substrate carrier  225  described above in connection with the electromagnetic embodiment. (When the voltage to the electrostatic plate  219  is turned off, the attractive force is eliminated.) Similarly, the pusher  220   b  can be used like the pusher  220  of  FIG. 2  to reduce the risk of dislodging the substrate carrier  225   b  from its intended position as the spatula  205   b  is withdrawn. The pusher  220   b  can be actuated like its counterpart  220  of  FIG. 2 . 
     Additional Mechanical Details 
     Movement of the assembly  200  (and likewise, assemblies  200   a  and  200   b ) is now described with respect to  FIGS. 5A and 5B .  FIG. 5A  shows the assembly  200  in combination with other components designed to permit the 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. 5B , which shows the assembly  200 , an upper carriage block  320 , a rail  325 , and a lower carriage block  330 . When these components are assembled, the assembly  200  can move along and over the rail  325 . 
     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 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 assembly  200 , thereby holding together the upper carriage block and the assembly. 
     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 . 
     As mentioned previously, once the substrate carrier  225  (or  225   a ,  225   b ) has been brought to an intended location, the pusher  220  is used to apply force against the substrate carrier while the spatula  205  is 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 spatula  205  is being retracted. One way to accomplish this is to synchronize the motion of the assembly  200  (with its spatula  205 ) 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 assembly  200 ) 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 assembly  200  retreats along the rail  325  at the same speed that the pusher  220  moves forward relative to the 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 assembly  200  and its spatula  205  (along with the upper carriage block  320  and the lower carriage block  330 ) are pushed away from the substrate carrier. 
     The various parts of the robotic device  110  (and the other robotic device embodiments described herein) may be machined from stock materials. The spatula  205  (and  205   a ,  205   b ) may be advantageously made of molybdenum, since it is thermally and mechanically stable. Alternatively, the spatula could be made from a ceramic material such as Macor® (although ceramics are more brittle), or it 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 assembly, such as the pusher  220  (or  220   a ,  220   b ), can be made of stainless steel, for example. The substrate carrier  225  (and  225   a ) is preferably fabricated from a magnetic material, and the substrate carrier  225   b  is preferably made from HAYNES® 230® alloy. The substrate carriers  225 ,  225   a , and  225   b  are preferably 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 devices 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. 
     The dimensions of the various parts disclosed herein may be selected in view of the intended application. A robotic device 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: an assembly ( 200 ,  200   a ,  200   b ) whose range of motion is between 200 mm and 600 mm, and a substrate carrier ( 225 ,  225   a ,  225   b ) having a width and a length of 20-60 mm. A larger device designed for manufacturing applications may have, for example: an assembly whose range of motion is between 600 mm and 1000 mm, an end effector whose width is less than 500 mm, and a substrate carrier having a width and a length of 300-500 mm. In either case, the range of motion of the pusher ( 220 ,  220   a ,  220   b ) is preferably at least that of the minimum lateral dimension of the substrate carrier. 
     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.