Abstract:
A multi-station measurement system concept is presented, particularly based on an X-Y stage and plurality of horizontal load/unload units. The system allows loading/unloading of wafers from several load/unload units by the direct action of the X-Y stage, thus creating a buffer for wafers without actually requiring an additional buffer mechanism.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to substrate processing systems and techniques, such as those used in semiconductor manufacturing and in particular to optical based processing such as metrology or inspection of semiconductor wafers. 
       BACKGROUND 
       [0002]    It is known in the art cluster measurement system including a measurement units and a wafer handling unit (Equipment Front-End Module “EFEM”) transferring wafers between measuring system(s) and wafer containers (FOUP&#39;s). Such a tool is known from U.S. Pat. No. 7,030,401 in the Name of Nanophotonics AG. Transfer means is arranged to transfer wafers between the containers and the measurement units through the handling unit. 
         [0003]    In order to reduce cycle time overhead, several separate metrology units are linked by an automation platform that handles wafer transport between the metrology units and a substrate container interface. Although the cluster tool is designed to provide increased throughput, the system is quite complex and expensive. 
       SUMMARY OF THE INVENTION 
       [0004]    It is the objective of the present invention to provide a solution for these problems by low cost and high reliability simple system configuration and operational sequence. In accordance with one general aspect of the invention is to provide a system of moderate cost and method of wafer handling for high throughput metrology tool. 
         [0005]    Generally, a multi-station measurement system concept is presented, particularly based on an X-Y stage and plurality of horizontal load/unload units. The system allows loading/unloading of wafers from several load/unload units by the direct action of the X-Y stage, thus creating a buffer for wafers without actually requiring an additional buffer mechanism. Such system configuration is thus capable of increasing throughput over standard system configurations, at a lower cost and higher reliability (lower number of moving parts), better utilizing throughput capacity of Wafer Transfer Robot. The system also supports measurements using a number of measuring channels without the need to reload or realign the wafer, thus, sharing wafer-handling resources (e.g. when one of the channels is infrequently used) and/or saving time (if several different measurements are required for the same wafer). Accordingly, this system potentially presents a lower cost-of-ownership for the end user in a large number of cases. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0006]    The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which: 
           [0007]      FIG. 1  is a schematic top view diagram showing a substrate measurement system according to a first embodiment, 
           [0008]      FIG. 2  is a schematic top view diagram showing a substrate measurement system according to second embodiment, and 
           [0009]      FIG. 3  presents timing charts of different system components. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  shows a substrate (a wafer W in the present embodiment) measurement system  10  comprising a wafer handling unit (EFEM)  12  provided with a wafer transfer means (single or multiple robot)  14  having one or more end-effectors (not shown). Term “measurement” also means inspection in the present invention. A unit  12  as a part of Equipment Front-End Module (“EFEM”) provides interface to the FAB and includes load ports for wafer cassettes (FOUP&#39;s)  16 . Wafer transfer means  14  provides wafers transferring from the cassettes  16  to load/unload units  18   a  and/or  18   b  of a measurement unit (MU)  20  preferably provided by a X-Y stage  21 . System  10  could be provided with graphical user interface (GUI)  22  and additional optional features such as aligner and ID reader (not shown). 
         [0011]    Plurality of load/unload units  18   a  and  18   b  (two in the present example) are substantially separated in horizontal plane and designed for receiving/unloading wafers from/to end-effectors of robot  14 . Also, load/unload units  18   a ,  18   b  provides wafers transferring onto/from stage  21  of MU  20 . Optionally, each or one of load/unload units  18   a    18   b  could include additional means  24  providing additional functionalities such as notch finding and ID reading, etc. The vertical transfer of wafers between load/unload units  18   a    18   b  and X-Y stage  21  could be done either by using loading/unloading units with wafer handling assembly having Z-axis movement actuator or by providing X-Y stage with additional movable Z-axis (not shown). 
         [0012]    Examples of appropriate wafer handling assembly and stage could found in U.S. Pat. No. 6,964,276 in the name of Nova Measuring Instruments Ltd incorporated herein by reference. X-Y stages used in the field are equipped with a mechanism for holding/transferring wafers that has sufficient travel range to enable pick and transfer wafers from/to different locations, in the present invention plurality loading units. Common used vacuum, edge gripping or other type chuck could be used for wafer holding. X-Y stage  21  generally provides moving wafer W in horizontal plane for bringing each point on the wafer (within a pre-define area on the wafer, e.g. excluding edge exclusion zone) to one or more measuring position(s)  26   a - 26   f  enabling measurement using one or more of the measurement channels (not shown) accordingly. Optionally, X-Y stage  21  could be also equipped with a rotation (theta) mechanism, enabling rotation of the wafer by 90 or 180 degrees thereby reducing the range of the X-Y travel (e.g. about radius of wafer W) and footprint accordingly. Rotation is required in order to enable scanning the entire or desired surface area of wafer W. 
         [0013]    One or more measurement channels  26   a - 26   f  (six in the present example) could provide either measurement or inspection of at least part of the wafer based on Spectral Reflectometry, Ellipsometry, Spectral Ellipsometry, a laser-based optical system, VUV, X-ray, etc. Measurement channels with measuring position(s)  26   a - 26   f  could provide various thin film parameters including optical characteristics and other parameters, OCD, defect inspection, overlay measurement, measurement of crystal parameters. Additionally, measuring channels could provide vision and/or alignment, etc. 
         [0014]    Circles C in dash lines in  FIG. 1  show the extreme wafer positions provided by X-Y stage  21  while scanning wafer W. A rectangle R shows the range in which the center of X-Y stage  21  (generally corresponding to the center of wafer W) should travel in order to cover all required measurement positions, entire wafer surface in the present example. 
         [0015]    In accordance with the present invention, configuration of system  10  provides a buffering for incoming and outgoing wafers W, potentially separating the operation of MU  20  from operation of wafer transfer robot  14  of the EFEM  16 . Such separation allows optimization of the overall system throughput as will be demonstrated furtherbelow. 
         [0016]    In accordance with one aspect of the present invention, as illustrated in  FIG. 1  the system  10  includes an X-Y-Theta stage providing a travel range which is slightly larger than the wafer diameter in the X direction and slightly larger than 1.5 the wafer W diameters in the Y direction. This configuration allows at least six different potential measurement positions where scanning the whole wafer at the central two position is done by X-Y and 180 rotation while for scanning the full wafer at the outer four positions also 90 degree rotations are required (which are not suitable for some measurement channels, such as Ellipsometry). This system is also could be equipped with a dual-blade robot  14  and load/unload units  18   a  and/or  18   b  providing wafer W notch-finding functionality. 
         [0017]      FIG. 2  illustrates yet another embodiment of the present invention. In this case a measurement system  100  includes X-Y stage  210  with increase range of Y-axis motion in order to provide “pure” X-Y scanning under the measurement position  260  without the need to use a rotation (theta) stage. Two configurations of  FIG. 1  and  FIG. 2  could be combined, creating a measurement system that supports one measurement position which is scanned by only X-Y motion and addition measurement positions which can be used with the help of some rotation motion (90 or 180 degrees). Circles C′ in dash lines show the extreme wafer positions provided by X-Y stage  210  while scanning wafer W. 
         [0018]    A typical time sequence that utilizes the capabilities systems  10  and  100  is illustrated in  FIG. 3 . The sequence includes the following steps: 
         [0019]    1. Starting position: One wafer located on chuck of X-Y stage  21  ( 210 ) and measurement is performed. Second wafer is loaded on load/unload unit  18   a , after optional Notch finding (alignment). Third wafer is held by one of the robot&#39;s  14  arms positioned next to load/unload unit  18   b.    
         [0020]    2. Measurement performed. 
         [0021]    3. X-Y stage  21  ( 210 ) moves to load/unload unit  18   b  and unloads the measured wafer thereon. 
         [0022]    4. X-Y stage  21  ( 210 ) moves to load/unload unit  18   a  and loads a wafer to be measured. 
         [0023]    5. MU  20  ( 200 ) performs measurement and to alignment and measurement. 
         [0024]    6. Robot  14  picks up measured wafer from load/unload unit  18   b  with empty arm. 
         [0025]    7. Robot  14  loads unmeasured wafer from first arm on load/unload unit  18   b.    
         [0026]    8. MU  20  ( 210 ) starts notch finding on wafer located on load/unload unit  18   b    
         [0027]    9. Robot  14  moves to one of FOUP&#39;s  16  and swaps wafers. 
         [0028]    10. Robot  14  moves back to waiting position next to load/unload unit  18   a    
         [0029]    11. End of cycle. 
         [0030]    As seen in  FIG. 3 , since three different operations could be actually performed in parallel, the system  10  ( 100 ) is optimized for throughput while leaving sufficient time for each operation to be successfully completed. Eventually this sequence allows the measurement channel (the “effective” part of the system) to be the bottleneck, rather than the wafer handling operations (the “overhead”) to be dominant. 
         [0031]    A limited number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.