Abstract:
An integrated system for processing a plurality of wafers, having a conductive front surface, is provided. The system includes a plurality of processing subsystems for depositing on or removing metal from the front surfaces of the wafers. Each processing subsystem includes a process chamber and a cleaning chamber. The system also has a wafer handling subsystem for transporting each of the wafers into or out of the appropriate one of the plurality of processing subsystems. The plurality of processing subsystems and wafer handling subsystem form an integrated system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation application of co-pending U.S. patent application Ser. No. 09/795,687, filed on Feb. 27, 2001, which claims priority to U.S. Provisional Application Nos. 60/259,676, filed Jan. 5, 2001, and 60/261,263, filed on Jan. 16, 2001. 
     
    
     BACKGROUND  
       [0002]     1. Field of the Invention  
         [0003]     The present invention generally relates to semiconductor processing technologies and, more particularly, to an integrated semiconductor wafer processing system.  
         [0004]     2. Description of the Related Art  
         [0005]     In the semiconductor industry, various processes can be used to deposit and etch materials on the wafers. Deposition techniques include processes such as electrochemical deposition (ECD) and electrochemical mechanical deposition (ECMD). In both processes, a conductor is deposited on a semiconductor wafer or a work piece by having electrical current carried through an electrolyte that comes into contact with the surface of the wafer (cathode). The ECMD process is able to uniformly fill the holes and trenches on the surface of the wafer with the conductive material while maintaining the planarity of the surface. A more detailed description of the ECMD method and apparatus can be found in U.S. Pat. No. 6,176,992, entitled “Method and Apparatus For Electrochemical Mechanical Deposition,” commonly owned by the assignee of the present invention.  
         [0006]     If a conventional plating process is performed to deposit the conductive material in a deposition chamber, the work piece may be transferred to another chamber in the cluster tool for polishing mechanically and chemically, e.g., chemical mechanical polishing (CMP). As is known, the material removal can also be carried out using electrochemical etching by making the wafer anodic (positive) with respect to an electrode after completing a ECD or ECMD process.  
         [0007]     Regardless of which process is used, the work piece is next transferred to a rinsing/cleaning station after the deposition and/or polishing steps. During the rinsing/cleaning step, various residues generated by the deposition and/or polishing processes are rinsed off the wafer with a fluid such as water or the like, and subsequently wafer is dried.  
         [0008]     Conventionally, processing chambers are designed in multiple processing stations or modules that are arranged in a cluster to form a cluster tool or system. Such cluster tools or systems are often used to process a multiple number of wafers at the same time. Generally, cluster tools are configured with multiple processing stations or modules and are designed for a specific operation. However in such conventional cluster tools, deposition and cleaning processing steps both typically require separate chambers. For this reason, in known cluster tools, for a wafer to be processed and cleaned, it must be moved to another station or system. Thus, such configured systems require picking wafers from a particular processing environment and placing into a cleaning environment. This may not be appropriate because during such transfer of the wafers, contaminants such as particles may attach themselves on the wafers. Additionally, such sequence of unloading, transporting, and reloading of the wafers may be costly and time consuming or require larger footprint.  
         [0009]     To this end, there is a need for alternative integrated processing systems which reduce manufacturing cost and increase manufacturing efficiency.  
       SUMMARY  
       [0010]     An integrated system for processing a plurality of wafers, having a conductive front surface, is provided. The system includes a plurality of processing subsystems for depositing on or removing metal from the front surfaces of the wafers. Each processing subsystem includes a process chamber and a cleaning chamber. The system also has a wafer handling subsystem for transporting each of the wafers into or out of the appropriate one of the plurality of processing subsystems. The plurality of processing subsystems and wafer handling subsystem form an integrated system.  
         [0011]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The above and other objectives, features, and advantages of the present invention are further described in the detailed description which follows, with reference to the drawings by way of non-limiting exemplary embodiments of the present invention, wherein like reference numerals represent similar parts of the present invention throughout several views and wherein:  
         [0013]      FIG. 1  illustrates a first embodiment of the present invention using a plurality of electrochemical deposition process stations;  
         [0014]      FIG. 2  illustrates a second embodiment of the present invention using a plurality of electrochemical mechanical deposition process stations;  
         [0015]      FIG. 3  illustrates a third embodiment of the present invention using a plurality of chemical mechanical processing process stations;  
         [0016]      FIG. 4  illustrates a fourth embodiment of the present invention using a plurality of electrochemical polishing or etching process stations;  
         [0017]      FIGS. 5 and 6  illustrate fifth and sixth embodiment of the present invention each using at least one plating process station and at least one conductor removal station;  
         [0018]      FIG. 7  illustrates a seventh embodiment of the present invention using a plurality of different process stations; and  
         [0019]      FIG. 8  illustrates an eighth embodiment of the present invention using a plurality of different process stations, including an anneal station. 
     
    
     DETAILED DESCRIPTION  
       [0020]     The present invention provides a system for semiconductor device fabrication. The system comprises several process modules to perform process steps such as electrochemical mechanical deposition (ECMD), electrochemical deposition (ECD), chemical mechanical polishing (CMP) and electrochemical polishing (EC-polishing) integrated with other process steps such as cleaning, edge removal and drying. Additionally, an integrated tool of the present invention is designed to utilize these process modules to perform multiple processing steps related to electrochemical deposition, chemical mechanical polishing, and electrochemical polishing.  
         [0021]     As mentioned above, following the ECD, ECMD, CMP or electrochemical polishing processes, the electrolyte residues need to be rinsed off the wafer, and subsequently wafer needs to be dried. Additionally, after such processes, it may be necessary to remove a portion of the metal that is deposited near the edge of the wafer surface. This process is often referred to as ‘bevel edge clean’ or ‘edge removal’ step. In the present invention, exemplary process chambers, i.e., ECD, ECMD, CMP or electrochemical polishing chambers, and their respective cleaning chambers are stacked vertically. In the prior art, however, the ECD process, electrochemical etching process, CMP process and cleaning process are carried at different chambers located horizontally with respect to each other. The edge removal step may be carried out in the cleaning chamber. In the context of this application, the cleaning chamber is the chamber where cleaning (using a fluid such as water or the like to remove residues therefrom) and drying and possibly edge removal process steps are performed.  
         [0022]     Reference will now be made to the drawings wherein like numerals refer to like parts throughout.  FIG. 1  illustrates an integrated tool  100  or system of the present invention which comprises a processing section  102  and a load/unload section  104  or a cassette section connected to the processing section through a buffer section  106 . The processing section may comprise one or more process stations  108 A- 108 D that may be clustered around the processing station  102 , as in the manner shown in  FIG. 1 . In this embodiment, the process stations  108 A- 108 D may preferably be vertically stacked chambers which may have a electrochemical deposition (ECD) chamber and a cleaning chamber (i.e., ECD/cleaning chamber). If so configured, the integrated tool  100  of the present invention is able to process wafers with different diameters. In one example, the process stations  108 A and  108 B can process 300 mm wafers while the process stations  108 C,  108 D are processing 200 mm wafers or vice versa. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in the co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of the present invention. In operation, wafers  110  or work pieces to be plated are delivered to the cassette section  104  in a cassette  112  and then each may be picked up and transferred to the buffer section  106  by a first robot  114 . Each wafer  110  can then be transferred to one of the vertical chambers  108 A- 108 D in the processing section  102  by a second robot  116 . As mentioned above, the vertical chambers  108 A- 108 D can be either adapted to process 200 or 300 millimeter wafers. After the electrochemical deposition and cleaning processes are complete, the above transport steps are performed in reverse order to remove each of the wafers from the integrated tool  100 .  
         [0023]      FIG. 2  illustrates another embodiment of an integrated tool  200  or system of the present invention which comprises a processing section  202  and a load/unload section  204  or a cassette section connected to the processing section through a buffer section  206 . The processing section may comprise one or more process stations  208 A- 208 D which may be clustered around the processing section  202 , as in the manner shown in  FIG. 2 . In this embodiment, the process stations  208 A- 208 D may preferably be vertically stacked chambers which may have a electrochemical mechanical deposition (ECMD) chamber and a cleaning chamber (i.e., ECMD/cleaning chamber), which can perform either plating or removal of a conductive material on a workpiece, as described in U.S. Pat. No. 6,176,992 mentioned above. If so configured, the integrated tool  200  of the present invention is able to process wafers with different diameters. In one example, the process stations  108 A and  108 B can process 300 mm wafers while the process stations  108 C,  108 D are processing 200 mm wafers or vice versa. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in the co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of the present invention.  
         [0024]     In operation, wafers  210  or work pieces to be plated with a conductive material and/or have a previously deposited conductive material disposed thereon are picked up and delivered to the cassette section  204  in a cassette  212  and then each may be transferred to the buffer section  206  by a first robot  214 . Each wafer  210  may then be transferred to one of the vertical chambers  208 A- 208 D, in the processing section  202  by a second robot  216 . As mentioned above, the vertical chambers  208 A- 208 D can be either adapted to process 200 or 300 millimeter wafers. After the plating and/or removal and cleaning processes are complete, the above transport steps are performed in reverse order to remove each of the wafers  210  from the integrated tool  200 .  FIG. 3  illustrates another embodiment of an integrated tool  300  or system of the present invention which comprises a processing section  302  and a load/unload section  304  or a cassette section connected to the processing section through a buffer section  306 . The processing section  302  may comprise one or more process stations  308 A- 308 B which may be clustered around the processing section  302 , as in the manner shown in  FIG. 3 . In this embodiment, the process stations  308 A,  308 D may preferably be vertically stacked chambers which may have a chemical mechanical polishing (CMP) chamber and a cleaning chamber (i.e., CMP/cleaning chamber). If so configured, the integrated tool  300  of the present invention is able to process wafers with different diameters. In one example, the process stations  308 A and  308 B can process 300 mm wafers while the process stations  308 C,  308 D are processing 200 mm wafers or vice versa. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in the co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of the present invention.  
         [0025]     In operation, wafers  310  or work pieces to be polished are delivered to the cassette section  304  in a cassette  312  and then each may be picked up transferred to the buffer section  306  by a first robot  314 . Each wafer  310  may then be picked up and transferred to one of the vertical chambers  308 A- 308 D in the processing section  302  by a second robot  316 . As mentioned above, the vertical chambers  308 A- 308 D can be either adapted to process 200 or 300 millimeter wafers. After the chemical mechanical polishing and cleaning processes are complete, the above transport steps are performed in reverse order to remove each of the wafers  310  from the integrated tool  300   FIG. 4  illustrates another embodiment of an integrated tool  400  or system of the present invention which comprises a processing section  402  and a load/unload section  404  or a cassette section connected to the processing section through a buffer section  406 . The processing section  402  may comprise one or more process stations  408 A- 408 D which may be clustered around the processing section  402 , as in the manner shown in  FIG. 4 . In this embodiment, the process stations  408 A- 408 D may preferably be vertically stacked chambers which may have an electrochemical polishing or electrochemical etching chamber and a cleaning chamber (i.e., EC-polishing/cleaning chamber). If so configured, the integrated tool  400  of the present invention is able to process wafers with different diameters. In one example, the process stations  408 A and  408 B can process 300 mm wafers while the process stations  408 C,  408 D are processing 200 mm wafers or vice versa. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of the present invention.  
         [0026]     In operation, wafers  410  or work pieces to be electrochemically polished are delivered to the cassette section  404  in a cassette  412  and then each may be transferred to the buffer section  406  by a first robot  414 . Each wafer  410  may then be picked up and transferred to the vertical chambers  408 A- 408 D in the processing section  402  by a second robot  416 . As mentioned above, the vertical chambers  408 A- 408 D can be either adapted to process 200 or 300 millimeter wafers. After the EC polishing and cleaning processes are complete, the above transport steps are performed in reverse order to remove each of the wafers  410  from the integrated tool  400 .  
         [0027]     While it is apparent from the above discussions that an advantage of the present invention is reducing contaminants as well as the time consumed, since the number of operations that can take place within the same vertical chamber therefore do not require the robots to handle the wafers as much, when vertical chambers which have different processing capabilities are made part of the integrated system, even further advantages are obtained in terms of overall throughput and reduced contamination. This is because within each of the different plating and removal chambers that are associated with a single processing section, there is also associated a cleaning chamber. Accordingly, the amount of time that would otherwise be needed to transfer wafers from one processing chamber, to a different cleaning chamber, and then again to a different processing chamber are eliminated, as will become more apparent hereinafter.  
         [0028]      FIG. 5  illustrates another embodiment of an integrated tool  500  or system of the present invention which comprises a processing section  502  and a load/unload section  504  or a cassette section connected to the processing section through a buffer section  506 . The processing section  502  may comprise one or more process stations  508 A,  508 B and  509 A,  509 B which may be clustered around the processing section  502 , as in the manner shown in  FIG. 5 . In this embodiment, the process stations  508 A,  508 B and  509 A,  509 B may preferably be vertically stacked chambers. The vertically stacked chambers may be arranged as a set of ECD/cleaning chambers  508 A,  508 B and a set of CMP/cleaning chambers  509 A,  509 B. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in the co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of the present invention.  
         [0029]     In operation, wafers  510  or work pieces to be plated and polished are delivered to the cassette section  504  in a cassette  512  and then each may be transferred to the buffer section  506  by a first robot  514 . Each wafer  510  may then be picked up and transferred to one of the vertical chambers  508 A,  508 B and  509 A,  509 B by a second robot  516 . In one example, the second robot  516  may initially transfers the wafers  510  to ECD/cleaning chamber  508 A. Once the plating by deposition and an initial cleaning is over, the second robot  516  picks up the wafers and transfers them to the CMP/cleaning chamber  509 A. After the chemical mechanical polishing and cleaning processes performed within the CMP/cleaning chamber  509 A are complete, the second robot  516  and then the first robot  514  consecutively handle each wafer  510  to replace the wafer in the cassette  512  of the integrated tool  500 . As mentioned above, the vertical chambers  508 A,  508 B or  509 A,  509 B can be either adapted to process 200 or 300 millimeter wafers.  
         [0030]      FIG. 6  illustrates another embodiment of an integrated tool  600  or system of the present invention which comprises a processing section  602  and a load/unload section  604  or a cassette section connected to the processing section through a buffer section  606 . The processing section  602  may comprise one or more process stations  608 A,  608 B and  609 A,  609 B which may be clustered around the processing section  602 , as in the manner shown in  FIG. 6 . In this embodiment, the process stations  608 A,  608 B and  609 A,  609 B may preferably be vertically stacked chambers. The vertically stacked chambers may be arranged as a set of ECD/cleaning chambers  608 A,  608 B and a set of EC-polishing/cleaning chambers  609 A,  609 B. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in the co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of the present invention.  
         [0031]     In operation, wafers  610  or work pieces to be plated and electrochemically polished and/or etched are delivered to the cassette section  604  in a cassette  612  and then each may be transferred to the buffer section  606  by a first robot  614 . Each wafer  610  may then be picked up and transferred to one of the vertical chambers  608 A,  608 B and  609 A,  609 B by a second robot  616 . In one example, the second robot  616  may initially transfer each of the wafers  610  to ECD/cleaning chamber  608 A. Once the plating and subsequent initial cleaning take place within the ECD/cleaning chamber  608 A, the second robot  616  picks up each of the wafer  610  and transfers it to the EC-polishing/cleaning chamber  609 A. After the EC-polishing and cleaning processes performed within the EC-polishing/cleaning chamber  609 A are complete, the second robot  516  and then the first robot  514  consecutively handle each wafer  610  to replace the wafer in the cassette  612  of the integrated tool  600 . As mentioned above, the vertical chambers  608 A,  608 B or  609 A,  609 B can be either adapted to process 200 or 300 millimeter wafers.  
         [0032]      FIG. 7  illustrates another embodiment of an integrated tool  700  or system of the present invention which comprises a processing section  702  and a load/unload section  704  or a cassette section connected to the processing section through a buffer section  706 . The processing section  702  may comprise a first, second, third and fourth process station  708 A,  708 B,  708 C and  708 D which may be clustered around the processing section  702 , as in the manner shown in  FIG. 7 . In this embodiment, the process stations  708 A- 708 D may preferably be vertically stacked chambers. The first station  708 A may be comprised of an ECD/cleaning vertical chamber. The second station  708 B may be comprised of an ECMD/cleaning vertical chamber. The third station  708 C may be comprised of a CMP/cleaning vertical chamber. The fourth chamber  708 D may be comprised of an EC-polishing/cleaning vertical chamber. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in the co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of this invention.  
         [0033]     In operation, wafers  710  or work pieces to be plated (with ECD and/or ECMD) and electrochemically polished or CMP polished are delivered to the cassette section  704  in a cassette  712  and then each may be transferred to the buffer section  706  by a first robot  714 . Each wafer  710  may then be picked and transferred to one of the vertical chambers  708 A- 708 D by a second robot  716 .  
         [0034]     In one example, the second robot  716  may initially transfer the wafer  710  to ECMD/cleaning chamber  708 B. Once the plating and/or electropolishing, and then an initial cleaning is performed within the ECMD/cleaning chamber  708 B the second robot  716  picks up the wafer  710  and transfers it to the CMP/cleaning chamber  708 C or EC-polishing/cleaning chamber  708 D. After either chemical mechanical polishing and cleaning, or EC-polishing and cleaning, performed by CMP/cleaning chamber  708 C or EC-polishing/cleaning chamber  708 D, respectively, is complete, are complete, the second robot  716  and then the first robot  714  consecutively handle each wafer  710  to replace the wafer in the cassette  712  of the integrated tool  700 .  
         [0035]     In a second example, the second robot  716  may initially transfer the wafer  710  to ECD/cleaning chamber  708 A. Once the plating and initial cleaning is performed within the ECD/cleaning chamber  708 A, the second robot  716  picks up the wafer  710  and transfers it to the CMP/cleaning chamber  708 C or EC-polishing/cleaning chamber  708 D. After the chemical mechanical polishing and cleaning or EC polishing and cleaning processes, performed by the CMP/cleaning chamber  708 C or EC-polishing/cleaning chamber  708 D, respectively are complete, the second robot  716  and then the first robot  714  consecutively handle each wafer  710  to replace the wafer in the cassette  712  the integrated tool  700 .  
         [0036]     As mentioned above, the vertical chambers  708 A,  708 B or  708 C,  708 D can be either adapted to process 200 or 300 millimeter wafers. Although the above embodiments exemplified with four process stations, it is understood that the use of more than four, for example six, process chambers is within the scope of this invention.  
         [0037]     It is also within the scope of the present invention that the above systems may also comprise an annealing chamber to anneal the wafers. When an anneal chamber is included, it is preferable to have the anneal chamber located in proximity to the buffer area, and for the anneal chamber to include both a “hot” section capable of heating the wafer, and a “cool” section capable of cooling the wafer after annealing has been completed. Such an anneal chamber will typically have the ability to operate upon a single wafer at a time, and is well known. Thus, further description is not believed necessary. What is advantageous with respect to the present invention is the manner in which the anneal chamber is integrated with the other processing sections, in order to maximize efficiency and throughput.  
         [0038]     Depending upon the construction of the system, it may be that only one of both of the robots can be constructed to place wafers into or take wafers out of the anneal chamber. If both robots can perform such operation, as described below, then if there are no further operations after annealing, as will be described hereinafter, the anneal chamber can act as a substitute buffer area.  
         [0039]      FIG. 8  illustrates an embodiment of an integrated tool  800  or system of the present invention using an anneal chamber as described above which comprises a processing section  802  and a load/unload section  804  or a cassette section connected to the processing section through a buffer section  806 . The processing section  802  may comprise a first, second, third, fourth and fifth process station  808 A,  808 B,  808 C,  808 D and  808 E which may be clustered around the processing section  802 , as in the manner shown in  FIG. 8 . The first station  808 A may be comprised of an ECD/cleaning vertical chamber or an ECMD/cleaning vertical chamber (both may also be used in a larger system) capable of operating upon 200 mm wafers. The second station  808 B may be comprised of an ECD/cleaning vertical chamber or an ECMD/cleaning vertical chamber (both may also be used in a larger system) capable of operating upon 300 mm wafers. The third station  808 C may be comprised of a CMP/cleaning vertical chamber or an EC-polishing/cleaning vertical chamber (both may also be used in a larger system), capable of operating upon 200 mm wafers. The fourth station  808 D may be comprised of a CMP/cleaning vertical chamber or an EC-polishing/cleaning vertical chamber (both may also be used in a larger system), capable of operating upon 300 mm wafers. As previously mentioned, one such exemplary vertical chamber design and operation is disclosed in co-pending U.S. application Ser. No. 09/466,014, entitled “Vertically Configured Chamber Used for Multiple Processes,” filed Dec. 17, 1999, commonly owned by the assignee of this invention. The fifth chamber  808 E may be comprised of an annealing chamber, as described above.  
         [0040]     In operation, wafers  810  or work pieces to be plated (with ECD and/or ECMD) are delivered to the cassette section  804  in a cassette  812  and then each may be transferred to the buffer section  806  by a first robot  814 . Each wafer  810  may then be picked up and transferred to one of the vertical chambers  808 A- 808 E by a second robot  816 .  
         [0041]     In one example, the second robot  816  may initially transfer each wafer  810  to one of the ECMD/cleaning chambers  808 A and  808 B, depending upon the size of the wafer. Once the plating and/or removal of conductive material from the front surface of the wafer and an initial cleaning is performed within the ECMD/cleaning chamber  808 A or  808 B, the second robot  816  picks up the wafer  810  and transfers it to the annealing chamber  808 E. Once annealed and chilled within the annealing chamber, the wafer  810  can then be picked up by the second robot  816  and transported to one of the CMP/cleaning chambers or EC-polishing/cleaning chambers  808 C or  808 D, depending upon the size of the wafer. Once conductive material is removed from the front face of the wafer using either the CMP/cleaning chamber or EC-polishing/cleaning chamber from  808 C or  808 D, and the subsequent cleaning within that same vertical chamber is completed, the second robot  816  and then first robot  814  can cooperate to transfer the wafer back to the cassette section  804 . As another example, if after the anneal there is not need for further processing, the wafer can be picked up from the anneal chamber by the first robot  814  and transferred directly back to the cassette section  804 .  
         [0042]     In the various embodiments mentioned above, it has been noted that the present invention is capable of operating upon different sized wafers, which wafers are placed into a cassette section. The size of the wafer in each of the different cassette is known, such as through the use of a software tag that is used by a system controller. Further, the robot arms that lift the wafers are configured so that they can detect the center of each wafer, regardless of size, and properly pick the wafer up.  
         [0043]     In addition, for each wafer, the system controller is also loaded with the process sequence, or recipe, that is needed for that wafer, with various portions of the process sequence performed by different processing stations. When sending a particular wafer to a particular processing station, that portion of the recipe can be sent in a command by the system controller to a processing station module, and that process can then take place, which then also allows tracking of the wafers that are being routed.  
         [0044]     While in a production environment it is typical for each wafer to have the same process sequence, and that is contemplated by the present invention as well, in certain research settings, have more control over the processing of each wafer has been found beneficial. Thus, as each wafer is transported to the appropriate processing station, which can include processing stations of the same type which operate upon different sized wafers, the system controller will track the progress of the wafer through the system, so that coordination of the transport of the wafer from processing station to processing station can occur.  
         [0045]     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.