[0001]    This application is a divisional of co-pending U.S. patent application Ser. No. 09/562,252, filed May 2, 2000, which is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE DISCLOSURE  
         [0002]    1. Field of Invention  
           [0003]    Embodiments of the present invention generally relates to a method for loading substrates into a semiconductor processing system.  
           [0004]    2. Background of Invention  
           [0005]    In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.  
           [0006]    Two exemplary CMP systems that address these issues are described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov et al. and in U.S. Pat. No. 5,738,574, issued Apr. 15, 1998 to Tolles et al, both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization system that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. The transfer station generally contains a load cup that positions wafers into one of four processing heads mounted to a carousel. The carousel moves each processing head sequentially over the load cup to receive a wafer. As the processing heads are loaded, the carousel moves the processing heads and wafers through the planarization stations for polishing. The wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry or other polishing fluid medium. The polishing pad may include an abrasive surface. The slurry typically contains both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.  
           [0007]    Generally, the wafer cassettes remain in the bath during operation of the system. As the wafers are polished, the system eventually requires that the cassettes containing polished wafers be removed from the bath to create space for new cassettes containing unpolished wafers. During the process of loading the bath, the system is shut down to prevent accidental interaction between operators exchanging cassettes in the bath and robotic equipment used to retrieve wafers from the bath. During this period, no wafers are processed resulting in the loss of valuable production time and factory capacity (i.e., adversely affecting substrate throughput).  
           [0008]    Therefore, there is a need in the art for method that loads substrates in a chemical mechanical polishing system having minimal impact on substrate throughput.  
         SUMMARY OF INVENTION  
         [0009]    One aspect of the present invention generally provides an apparatus for loading a semiconductor processing system. In one embodiment, a loader includes a wall having an exterior side with one or more apertures formed therethrough. A door assembly is movably coupled to the wall in each of the apertures and is adapted to temporarily retain substrates. A first portion of the door assembly substantially closes the aperture when the door assembly is in a first or closed position, and a second portion of the door assembly substantially closes the aperture when the door assembly is in a second or open position.  
           [0010]    In another embodiment of the invention, a loader may further include a wafer mapper, an interlock, a wafer sensor and a wetting system. The loader may additionally be coupled to a factory interface and one or more polishing modules having a robot positioned therebetween. The robot transfers the wafers between the one or more polishing modules and the substrate storage cassette.  
           [0011]    In yet another embodiment, the invention provides a robot for transferring a substrate in a processing system. The robot includes a central body having a shaft rotationally extending therefrom. An arm coupled at a proximate end to the shaft by a rotary actuator. A gripper is coupled to a distal end of the arm.  
           [0012]    In another aspect of the invention, a method for loading a semiconductor processing system is provided. In one embodiment, a method for loading a processing system includes providing a first substrate cassette supported by a door assembly in a position where substrates contained in the first substrate cassette may be accessed by a robot that transfers the substrates to a processing area for processing; moving the door assembly supporting the first substrate cassette to a position where the first substrate cassette may not be accessed by the robot; replacing the first substrate cassette with a second substrate cassette while the system continues to process other substrates; and returning the door assembly to the position where the second substrate cassette may be accessed by the robot.  
           [0013]    In another embodiment, the method includes providing a first substrate cassette having one or more substrates, securing the substrate with a gripper disposed at a distal end of an arm of a robot, removing the substrate from the cassette by a combined lateral movement of the robot and rotational movement of the arm about the center of the robot that produces a movement of the substrate substantially perpendicular to the lateral movement of the robot. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 is a plan view of a chemical mechanical planarization system having a substrate loader;  
         [0016]    [0016]FIG. 2 depicts one embodiment of a loading robot;  
         [0017]    [0017]FIG. 3A depicts a perspective view of the loader of FIG. 1;  
         [0018]    [0018]FIG. 3B depicts another perspective view of the loader of FIG. 1;  
         [0019]    [0019]FIG. 4 is an elevation of one embodiment of a loading assembly;  
         [0020]    [0020]FIG. 5 is a cross sectional view of the loading assembly taken along section line  5 - 5  of FIG. 4;  
         [0021]    [0021]FIG. 6A depicts a cross sectional view of the factory interface taken along section line  6 A- 6 A of FIG. 1;  
         [0022]    [0022]FIG. 6B depicts a cross sectional view of the factory interface taken along section line  6 B- 6 B of FIG. 1;  
         [0023]    FIGS.  7 A- 7 C depict a sequence of motion of the loading robot of FIG. 2; and  
         [0024]    [0024]FIG. 8 depicts another embodiment of a loading assembly. 
     
    
       [0025]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.  
       DETAILED DESCRIPTION OF INVENTION  
       [0026]    [0026]FIG. 1 depicts a plan view of a chemical mechanical planarization system  100 . The exemplary system  100  generally comprises a factory interface  102 , a loading robot  104 , and a polishing module  106 . Generally, the loading robot  104  is disposed proximate the factory interface  102  and the polishing module  106  to facilitate the transfer of substrates  122  therebetween.  
         [0027]    The factory interface  102  generally includes one or more door assemblies  130  where substrate storage cassettes  128  may be loaded into, or removed from the factory interface  102 . The substrate storage cassettes  128  hold substrates  122  before and after processing. Optionally, the factory interface  102  may include substrate cleaning modules, queuing stations, plating modules and metrology modules.  
         [0028]    A controller  108  is provided to facilitate control and integration of the modules comprising the system  100 . The controller  108  comprises a central processing unit (CPU)  110 , a memory  112 , and support circuits  114 . The controller  108  is coupled to the various components of the system  100  to facilitate control of, for example, the polishing and transfer processes.  
         [0029]    One polishing module  106  that can be used to advantage with the present invention is a MIRRA® Chemical Mechanical Polisher, manufactured by Applied Materials, Inc., located in Santa Clara, Calif. Other polishing modules  102  including those that use polishing pads, polishing webs, or a combination thereof may also be used to advantage. Other systems that benefit include systems that move a substrate relative a polishing surface in a rotational, linear or in other polishing motion.  
         [0030]    The exemplary polishing module  106  has a transfer station  136 , a plurality of polishing stations  132  and a carousel  134  disposed on an upper or first side  138  of a machine base  140 . In one embodiment, the transfer station  136  comprises at least an input buffer station  142 , an output buffer station  144 , a transfer robot  146 , and a load cup assembly  148 . The loading robot  104  places the substrate  122  onto the input buffer station  142 . The transfer robot  146  has two gripper assemblies, each having pneumatic gripper fingers that grab the substrate  122  by the substrate&#39;s edge. The transfer robot  146  lifts the substrate  122  from the input buffer station  142  and rotates the gripper and substrate  122  to position the substrate  122  over the load cup assembly  148 , then places the substrate  122  down onto the load cup assembly  148 . An example of a transfer station that may be used to advantage is described by Tobin in U.S. patent application Ser. No. 09/414,771, filed Oct. 6, 1999, and is hereby incorporated by reference.  
         [0031]    Alternatively, the transfer station  136  may comprise a load cup assembly  148 . In such a configuration, the loading robot  104  places and retrieves the substrate  122  directly from the load cup assembly  148 .  
         [0032]    The carousel  134  is generally described by Tolles in the previously incorporated U.S. Pat. No. 5,804,507. Generally, the carousel  134  is centrally disposed on the base  140 . The carousel  134  typically includes a plurality of arms  150 , each supporting a polishing head assembly  152 . Two of the arms  150  depicted in FIG. 1 are shown in phantom such that a polishing surface  116  of one of the polishing stations  132  and the transfer station  136  may be seen. The carousel  134  is indexable such that the polishing head assemblies  152  may be moved between the polishing stations  132  and the transfer station  136 .  
         [0033]    The loading robot  104  is generally positioned proximate the factory interface  102  and the polishing module  106  such that the range of motion provided by the robot  104  facilitates transfer of the substrates  122  therebetween. The loading robot  104  may be any one of a number of robots having the range of motion that facilitates substrate transfer between the factory interface  102  and the polishing module  106 .  
         [0034]    [0034]FIG. 2 depicts one embodiment of the loading robot  104 . The loading robot  104  is coupled to a guide  202  that is movably coupled to a rail  204  disposed in an upper portion of the factory interface  102 . The rail  204  and guide  202  allow the loading robot  104  to move along the factory interface  102  or linearly (e.g., laterally) between the factory interface  102  and polishing module  106 . Alternatively, the loading robot  104  may be positioned proximate the factory interface  102  and operatively coupled to a linear actuator, a pneumatic cylinder, a hydraulic cylinder, a magnetic drive, a stepper or servo motor, or other type of motion device that may position the loading robot  104  relative the factory interface  104  and polishing module  106 .  
         [0035]    The loading robot  104  generally includes a central shaft  206  extending from a central body  220 . A proximate end  222  of an arm  210  is coupled to the shaft  206  by a rotary actuator  212 . The rotary actuator  212  allows the arm  210  to be “flipped” 180 degrees about the actuator  212 . The shaft  206  is rotatable such that the arm  210  may be rotated about the shaft  206 .  
         [0036]    A gripper  214  is disposed at a distal end  224  of the arm  210 . The gripper  214  secures the substrate  122  to the arm  210  during transfer to the substrate  122  between the factory interface  102  and the polishing module  106 . In one embodiment, the gripper  214  is a vacuum gripper. Optionally, other types of gripping mechanisms may be employed such as edge contact grippers, mechanical clamps, electrostatic chucks and other wafer retention devices.  
         [0037]    [0037]FIGS. 3A and 3B respectively depict front and back perspective views of the factory interface  102 . The factory interface  102  generally includes a frame  316  enclosed by sides  372 , a top  374  and an exterior side  316 . A backside  370  opposite the exterior side  316  of the factory interface  102  is open to the loading robot  104 . The exterior side  316  includes one or more apertures or bays  302  formed therein. Each loading bay  302  is adapted to accept the door assembly  130  that holds the substrate storage cassette  128 . The substrate cassettes  128  are orientated with an open end  326  exposed towards the backside  370  of the factory interface  102  to facilitate access by the loading robot  104 .  
         [0038]    The door assembly  130  positions the substrate cassettes  128  within the factory interface  102 . The door assembly  130  has a handle  320  disposed thereon to facilitate opening access to the substrate storage cassettes  128  by an operator or material handler. The handle  322  contains an interlock switch  376  coupled to the controller  108 . When an operator or material handler wishes to open the door assembly  130 , the switch  376  is actuated, signaling the controller  108  that the respective door assembly  130  is desired to be open. The controller  108  determines if the activity of the loading robot  104  is clear of the respective door assembly  130  (and associated cassette  128  positioned thereon) and unlocks the door assembly  130 , permitting the door assembly  130  to be opened. Alternatively, the door assembly  130  may be opened and closed using automated components. A pair of indicator lights  378  is provided on the door assembly  130  or exterior side  318  of the factory interface  102  to indicate the lock/unlocked status of the door assembly  130 . In one embodiment, the factory-interface  102  generally includes three door assemblies  306  disposed in a respective wafer loading bay  302 .  
         [0039]    [0039]FIGS. 4 and 5 generally depict the door assembly  130  in front and sectional views, respectively. The door assembly  130  generally includes a first portion  412  and a support plate  446  that are orientated substantially perpendicular to each other. One or more fillets  438  are disposed between the first portion  412  and the support plate  446 . The fillets  438  may be disposed between the first portion  412  and the support plate  446  to enhance the structural rigidity of the door assembly  130 . The door assembly  130  is rotatably coupled to the factory interface  104  by a hinge generally including shaft and bearing (not shown). A second portion  414  is coupled parallel to the support plate  446 . Optionally, the second portion  414  and the support plate  446  may be combined into a single structure. The term “substantially perpendicular” is intended to mean within a few degrees of perpendicular. Of course those skilled in the arts may configure the door assembly  130  utilizing other angles by accommodating different angles by varying the configuration of other components of the system  100 .  
         [0040]    The first portion  412  generally is fabricated from aluminum or other corrosion resistant material. The first portion  412  includes a wafer mapper  480 , a first locating rail  482  and a second locating rail  484 . The wafer mapper  480  is fastened to the first portion  412 . The wafer mapper  480  has a window  486  that shields two spaced-apart sensors  488 A and  488 B that are coupled to the controller  108 . The sensors  488 A,  488 B move within the mapper  480  to detect the presence of the substrates  122  in the cassette  128  viewed through the window  486 . The spaced-apart relation of the sensors  488 A,  488 B allow the controller  108  to additionally determine if a substrate is misaligned within the cassette  128  (i.e., the sensor  488 A detects a substrate at a vertical position different that sensor  488 B). The sensor  448  is coupled to the controller  108  to provide information regarding the presence of the substrate  122 . The information is used to sequence substrates  122  through the polishing module  106 , and to insure that substrates  122  returning from the polishing module  106  are placed in a vacant slot  516  of the cassette  128 .  
         [0041]    A blow-off bar  452  is movably mounted to the wafer mapper  480 . The blow-off bar  452  includes a plurality of nozzles  453  is coupled to a gas source that provides gas (e.g., air) which is used to clear the window  486  of excess fluids or other debris. The air flowing from the nozzles  453  substantially removes on liquids or contaminants that may be present on the window  486  to enhance the operation of the sensors  488 A,  488 B.  
         [0042]    The bar  452  is connected to a magnet  454  that rides in a track  456 . The magnet  454  is attracted to a drive system  458  that moves the sensors  488 A,  488 B in the mapper  480 . As such, the window  486  is continually cleared in the position required for the sensors  488 A,  488 B to sense the presence of the substrates  122  in the cassette  128 . Alternative means may be provided such that the nozzles  453  clean the portion of the window  486  through which the sensors  488 A,  488 B are operating.  
         [0043]    The rails  482 ,  484  and a tab  490  locate the cassette  128  in the door assembly  130  and are generally fabricated from plastic. The second rail  484  has an “L” section that contains a reflector  492  that interfaces with a sensor  502  disposed in the support plate  446 . When the cassette  128  is disposed properly in the door assembly  130  (i.e., set between the rails  482 ,  484 , the tab  490  and wafer mapper  480 ), the cassette  128  breaks the signal between the sensor  502  and reflector  492 , indicating the presence of the cassette  128 .  
         [0044]    The support plate  446  has a sensor  504  mounted at an outer end  506  of the support plate  446 . The sensor  504  directs a beam upward to detect a substrate  122 A that may be undesirably extending from the cassette  128 .  
         [0045]    The second portion  414  of the door assembly  130  is generally comprises of aluminum or other corrosion resistant material. The second portion  414  has a damping device coupled thereto. The damping device facilitates controlled movement of the door assembly  130 . The damping device may include springs, fluid cylinders, gas pots (gas spring), or other motion control devices. In one embodiment, the damping device is a gas pot  508  coupled between the second portion  414  and the exterior wall  316  of the factory interface  102 .  
         [0046]    An interlock pin  510  is movably disposed between the first portion  412  of the door assembly  130  and the exterior wall  316  to prevent the door assembly  130  from opening without prompting by the controller  108 . In one embodiment, the interlock pin  510  is disposed in a recess  514  in the first portion  412  of the door assembly  130 . Upon activation of the switch  376 , the controller  108  applies power to a solenoid  512  that pulls the pin  512  clear of the recess  514  to allow the door  130  to be opened. Alternatively, the pin  510  may be disposed between other components of the door assembly  130  to prevent undesired opening. A detector  520  may be optionally disposed proximate the interlock pin  510  to provide the controller  108  with information concerning whether the door assembly  130  is locked into position. The detector  520  may be disposed in the door assembly  103 , the wall  316  or be part of the solenoid  512  or the solenoid control circuitry. Optionally, other devices may be utilized to interlock the door assembly  130 .  
         [0047]    [0047]FIGS. 6A and 6B depict the factory interface  102  having the door assembly  130  in a first (open) and a second (closed) position, respectively. When the door assembly  130  is in the second or closed position, the first portion  412  is substantially vertical and co-planar with the exterior wall  318  of the factory interface  104 . The first portion  412  effectively blocks the bay  302 , shielding the interior of the factory interface  102 .  
         [0048]    When the door assembly  130  is in the open position, the substrate storage cassette  128  having the open end  326  facing upwards, may be set upon the now horizontal first portion  412 . The substrate storage cassette  128  is positioned against the second portion  414  such that the tab  490  extending from the second portion  414  retains the cassette  128  between the tab  490  and the wafer mapper  480 .  
         [0049]    While in the open position, the second portion  414  provides a barrier between the loading robot  104  and the exterior of the factory interface  104 , guarding (i.e., shielding) the operator from the moving components of the system  100 . As such, the system  100  may continue processing substrates  122  during material handling (i.e., substrate storage cassette change-out), thus enhancing the throughput of the system  100 . When the door assembly  130  is rotated to the closed position, the open end  326  of the cassette  128  is orientated horizontally towards the loading robot  104  to facilitate access by the robot  104  to the substrates  122 .  
         [0050]    Referring to FIG. 8 that depicts an alternative embodiment of a door assembly  830 , a first portion  802  and the second portion  804  are orientated vertically in the bay  302  formed in the exterior wall  316  of the factory interface  102 . The door assembly  830  has a rotation about a vertical axis to move between an open and a closed position. In such a configuration, the cassette  128  containing the substrates  122  is positioned on a support plate  806  disposed between the portions  802 ,  804 . Alternatively, one or both of the first or second portions  802 ,  804  may contain a catch (not shown) that supports the cassette  128  suspended therebetween.  
         [0051]    Returning to FIG. 6A, a substrate wetting system  608  is disposed in each bay  302 . Generally, the wetting system  608  includes a plurality of nozzles  630  disposed in one or more fluid supply lines  632  disposed in each bay  302 . The nozzles  630  are orientated such that a wetting fluid, such as de-ionized water, may be sprayed on the substrates  122  contained in the substrate storage cassettes  128  to prevent the substrates (and any materials or debris thereon) from drying without immersing the substrates  122  in a fluid bath. The fluid may be sprayed from the nozzles  630  continuously or at programmable intervals. In one embodiment, the substrate wetting system  608  is coupled to an interior wall  628  of each bay  302  and maintains both sides of the substrate  122  in a wet condition. The fluids and contaminants generated by the substrate wetting system  608  are typically collected in a catch basin  634  positioned at the bottom of the factory interface  104 . The catch basin  634  is coupled to a drain  636  that is typically connected to the facilities central drainage system (not shown). The catch basin  634  includes a fluid level sensor  602  that is coupled to the controller  108 . If excess fluids are present in the catch basin  634 , the sensor  602  indicates to the controller  108  that the fluid supply or drain systems have a malfunction and that the system  100  should be shut down. Optionally, the substrate wetting system  408  may include additional locations in each bay  302 .  
         [0052]    The factory interface  102  additionally includes a door assembly position indicator  640 . The door assembly position indicator  640  includes a sensor  642  mounted to the interior wall  428  of the bay  302 . The sensor  642  may be any number of sensors that can detect if the door assembly  130  is in the first (closed) position. For example, the sensor  642  may be a limit switch having a button  644  that is actuated by the second portion  414  of the door assembly  130  when the door assembly is moved into the first position. The sensor  642  is coupled to the controller  108  to provide the system  100  with information regarding whether the door assembly  130  is closed. Optionally, the controller  108  actuates an indicator light  644  disposed on the exterior of the factory interface  102  to indicate that the door assembly  130  is in the first position. Other examples of sensors  642  include proximity switches, photoelectric sensors, mechanical switches, magnetic contacts, hall effect switches and the like. Alternatively, the door assembly position indicator  640  may be mounted on the door assembly  130  or other location suitable for the type of sensor  642  selected.  
         [0053]    Referring to FIGS. 1, 6A and  6 B, in operation, the substrate  122  is retrieved from one of the cassettes  128  by the loading robot  104 . Since the arm  210  and gripper  214  remain fixed relative to each other, the gripper  215  must be directed into the cassette  128  the loading robot  104  by rotating the shaft  206  while translating the robot  104  along the rail  204 . The loading robot  104  transfers the substrate  122  to the transfer station  136  where the substrate  122  is loaded into one of the polishing head assemblies  156 . Before placing the substrate on the transfer station  136 , the loading robot  104  flips the substrate  122  from a horizontal, feature side-up orientation in the cassette  128  to a horizontal, feature side-down orientation in the transfer station  136  by actuating the rotary actuator  212  (see FIGS.  7 A- 7 C).  
         [0054]    The carousel  134  is indexed to position the polishing head assembly  152  and the substrate  122  over one of the polishing stations  132 . A drive system is actuated to place the substrate  122  in contact with the polishing surface  116 . In one embodiment, both the polishing head assembly  152  and the polishing surface  116  rotate, while the polishing head assembly  152  is oscillated along the arm  150  of the carousel  134 , thus providing the polishing motion of the substrate  122  relative the polishing surface  116 .  
         [0055]    Once polishing is completed, the substrate  122  is removed from the polishing surface  116  and indexed to another polishing station or returned to the transfer station  136 . Polished substrates  122  are retrieved from the transfer station  136  by the loading robot  104  and transferred to the factory interface module  102  where the substrate  122  is flipped feature side-up and ultimately returned to one of the storage cassettes  128  where the substrates  122  are maintained in a wet conduction by the wetting system  608 .  
         [0056]    Once the one of the substrate storage cassettes  128  has been emptied of unpolished substrates  122  and filled with polished substrates  122  returning from the polishing module  106 , the wafer mapper  480 , through the controller  108 , indicates that the cassette  128  is filled and is ready for change-out.  
         [0057]    The switch  376  is activated to open the door assembly  130 . After the controller  108  determines that if the door assembly  130  can be opened without risk of equipment or product damage, the interlock is released, removing the pin  510  that locks the door assembly  130  in the closed position. The door assembly  130  is then rotated from the first, closed position to the second open position, exposing the substrate storage cassette  128  containing the polished substrates  122  to the exterior  316  of the factory interface  102 . As the second portion  414  of the door assembly  130  shields the transfer robot  104  and other moving components of the system  100  from operators and material handlers on the exterior  318  of the factory interface  102 , the system  100  may continue processing other substrates  122  while the door assembly  130  is in the open position. The ability of the system  100  to maintain operation during storage cassette exchange enhances the throughput of the system  100 .  
         [0058]    The substrate storage cassette  128  is removed from the open door assembly  130  and replaced with another cassette  128  containing substrates  122  to be processed. The substrate storage cassette  128  containing the substrates  122  to be polished are placed in the door assembly  130  and located by the rails  482 ,  484  and tab  490 . The sensor  502  confirms that the cassette  128  is properly positioned. The door assembly  130  is then closed (i.e, returned to the closed position) wherein the interlock is re-engaged. The sensor  442  indicates that the door assembly  130  is in fully closed and that the substrates  122  are ready for processing. The wafer mapper  480  updates the controller  108  regarding the status of the substrates  122  in the cassette  128 . The loading robot  104  than accesses the substrates  122  for processing as described above.  
         [0059]    Although the teachings of the present invention that have been shown and described in detail herein, those skilled in the art can readily devise other varied embodiments that still incorporate the teachings and do not depart from the spirit of the invention.
A method for loading substrates in a processing system is provided. In one embodiment, a method for loading substrates utilizes a substrate loader that generally includes a wall having an exterior side with one or more apertures formed therethrough and a related method of loading a processing system. A door assembly is movably coupled to the wall in each of the apertures and is adapted to temporarily retain the substrate. A first portion of the door assembly substantially closes the aperture when the door assembly is in a first or closed position, and a second portion of the door assembly substantially closes the aperture when the door assembly is in a second or open position. A robot for transferring a substrate in a processing system is also provided.