Abstract:
An ion implantation apparatus is provided for workpiece handling. The apparatus includes a plurality of scan systems for scanning workpieces in an ion implanting beam, a plurality of exchangers for moving the workpieces to and from the scan systems, and a system controller for positioning one of the workpieces for scanning in the ion implanting beam by one of the scan systems, sensing completion of the ion beam scanning for the one workpiece and simultaneously positioning another of the workpieces for scanning in the ion implanting beam by another of the scan systems so that the workpieces are continuously presented to the ion implanting beam. The apparatus provides continuous implantation relative to the beam, thus enabling wafer exchange to occur in parallel with the implantation process. As a result, significant system productivity improvement and wafer throughput will be realized.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 60/527,977, filed Dec. 8, 2003, entitled “System and Method for Serial Ion Implanting Productivity Enhancements,” the disclosure of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The described system and method relate generally to maximizing the beam on wafer time during serial ion implantation processing. More particularly, the described system and method are directed to maximizing the presence of a wafer in front of the beam path so that the utilization of the beam for implanting is maximized.  
       BACKGROUND OF THE INVENTION  
       [0003]     The processing of semiconductor wafers involves processing tools for performing a large number of processing steps. The processing steps are usually performed in a vacuum chamber. The processing tools typically handle and process wafers one at a time in order to optimize control and reproducibility. These processing tools utilize automated wafer handling.  
         [0004]     The throughput of processing tools is an important factor in achieving low cost manufacture. Ion implantation processing is one such processing step in which the efficiency of the wafer handling is critical to the overall wafer throughput. Wafer handling involves introduction of the wafers in a cassette or other wafer holder into the processing tool. The processing tool will typically remove the wafers from the cassette or other wafer holder and transport the wafers in the vacuum chamber, typically through a load lock, and then further transfers the wafers to a processing station. Upon completion of processing the wafers, the wafer handler will transport the wafers back to the cassette or wafer holders. Some of the processing and wafer handling operations may be performed concurrently to achieve efficient operation and high throughput. Careful design of wafer handling systems is required and a variety of wafer handling techniques are known in the prior art.  
         [0005]     In one prior art system disclosed by Tamai in U.S. Pat. No. 5,929,456, a first group of wafers and a second group of wafers are rotated along first and second orbital paths intersecting a path of an ion beam during ion implantation processing. A wafer from each of the two groups is transferred to first and second wafer holders that respectively move the wafers on orbital paths CL1 and CL2 with at least a portion of the second orbital path being different from the first orbital path as shown in FIGS. 1A-1D of the Tamai patent. After one of the wafers completely traverses an ion beam radiation region 4, the wafer is transported upward as indicated by the broken lines in FIGS. 1B and 1D, while the other wafer traverses the radiation region. These processes are repeated until ion implantation of the two wafers is completed. Once the two wafers are implanted, two new wafers are transferred from load locks to replace the two implanted wafers on the wafer holders 50A and 50B. The two wafers are continuously rotated in front of the ion beam until the ion implantation processing is completed. Once the ion implantation processing is completed, the next set of unprocessed wafers replaces the processed wafers. These cycles are repeated until all of the wafers from the load lock are processed. However, this system suffers from relatively low wafer throughput because the ion beam is not fully utilized. During transfer of the sets of wafers, the beam is not being utilized for implanting into the wafer. Accordingly, there is a need for improved wafer handling systems which maximize the utilization and the time that ion beam is implanting onto the wafers or workpieces.  
       SUMMARY OF THE INVENTION  
       [0006]     In serial implant ion implanters, the ion beam utilization is low. This is due to the presence of a wafer holding device, or platen, for processing (ion implanting) and wafer exchange. The time to exchange a processed wafer to an unprocessed wafer is in series with the implant process. The utilization of the ion beam on wafer is poor due to wafer exchange occurring in the critical path of the implantation process. This reduces the potential system throughput due to ion beam non-utilization during wafer exchange. The present invention is directed to utilizing a plurality of single wafer holding devices to approach continuous implantation relative to the beam, thus enabling wafer exchange to occur in parallel with the implantation process. As a result, significant system productivity improvement and wafer throughput will be realized.  
         [0007]     According to a first aspect of the invention an ion implantation apparatus is provided for workpiece handling. The apparatus comprises a plurality of scan systems for scanning workpieces in an ion implanting beam, a plurality of exchangers for moving the workpieces to and from the scan systems, and a controller for positioning one of the workpieces for scanning in the ion implanting beam by one of the scan systems, sensing completion of processing for the one workpiece and simultaneously positioning another of the workpieces for scanning in the ion implanting beam by another of the scan systems so that the workpieces are continuously presented to the ion implanting beam. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein:  
         [0009]     FIGS.  1 ( a )- 1 ( g ) show examples of a two platen serial ion implanter according to embodiments of the present invention; and  
         [0010]      FIG. 2  is a flow chart illustrating processing steps performed by a dual platen serial ion implanter according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]     According to the present invention, a system is provided for a high efficiency utilization of an ion beam while implanting semiconductor wafers. FIGS.  1 ( a )- 1 ( g ) illustrate examples of a system  100  for a two platen serial ion implanter according to an embodiment of the present invention. The system includes a load lock  110  for holding pass through cassettes of workpieces or wafers, which are passed from atmosphere (load area) to a vacuum area (implanting area) and then back after the ion implanting process is completed. First and second workpiece exchangers  120  and  122  are positioned between the load lock  110  and the first and second platens  130  and  132  for moving workpieces therebetween. The first and second workpiece exchangers  120  and  122  may be dual arm, multi-link or scara robots or the equivalent workpiece/wafer moving devices. In the present embodiment, the load lock  110  includes two load lock chambers  112  and  114  which are associated with the first and second platens  130  and  132 . It should be realized by one skilled in the art that the number of load lock chambers may vary and is related to the complexity and sophistication of the first and second exchangers  120  and  122 .  
         [0012]     First and second scan systems  140  and  142  are associated with the first and second exchangers  120  and  122  respectively. The first and second scan systems  140  and  142  support platens  130  and  132  (also known as wafer holding devices) in which the first and second exchangers  120  and  122  exchange a processed workpiece with an unprocessed workpiece. The first and second scan systems  140  and  142  have a minimum of three axis, to allow the respective one of the first and second scan systems  140  and  142  to be rotated and translated up and down so that the workpiece may move through the transfer, queuing and implanting positions which will be described in more detail with respect to specific embodiments of the present invention. A system processor/controller  150  controls the movement of the workpieces between the first and second exchangers  120  and  122 , the first and second scan systems  140  and  142  as well as the load lock  110 . The ion beam  102  used for ion implantation may be a ribbon beam, a spot beam or the like as are known to those skilled in the art. The first and second scan systems  140  and  142  may scan the workpieces either horizontally, vertically or at predetermined angles relative to the ion beam  102  as desired for the particular implanting/processing application.  
         [0013]      FIG. 2  illustrates a flow chart for one embodiment of the present invention utilizing a dual platen scan system. Step  200  of this flow chart represents processing in the steady state condition of a wafer on the first platen  130  completing its last pass of an implant and a wafer on the second platen  132  beginning the first pass of an implant. For simplicity, it is assumed that after either the first or second exchanger  120  or  122  exchanges a processed wafer for an unprocessed wafer at a respective platen, the processed wafer is then exchanged for an unprocessed wafer at the load lock  110 . At step  210 , a wafer on the first platen  130  moves to the wafer exchange position. During step  220 , the first exchanger  120  exchanges the processed wafer with an unprocessed wafer at the first platen  130 . The first scan system  140  moves the first platen  130  with the unprocessed wafer into a pre-implant position at step  230 . Steps  210 ,  220 , and  230  occur concurrently while the wafer on the second platen  132  is implanted at step  250 . These steps and processes are generally represented in FIGS.  1 ( a )- 1 ( d ). The exchangers and scan systems for the platens have a sufficient number of degrees of freedom for positioning the wafer as required.  
         [0014]     Next, the system controller  150  determines whether the wafer on the second platen  132  is completing the last implant pass at step  240 . As one of the goals of the present invention is to have a wafer continuously scanning in the ion beam  102 , the next wafer cannot be moved into the ion beam path  102  until the implanting process for the previous wafer is completing the last pass of a scan. For instance, the system controller  150  generates a signal to indicate when the last implant pass is completing for the wafer on the processing platen, which also indicates that the wafer on the other platen is ready for implanting. Multiple passes of the ion beam  102  across the wafer are often necessary to ensure sufficient and uniform implant dose. For example, in high throughput conditions, one scan (one scan equals two wafer passes through the ion beam) is required, however depending on the beam current and dose required, more than one scan may be required. If the wafer on the second platen  132  is not completing the last pass, then the wafer on the first platen  130  waits in the pre-implant position so as to not interfere with the on going implant process at step  250 . The system controller  150  continually monitors the on-going implant at step  240 .  
         [0015]     As the wafer on the second platen  132  enters the last implant pass at step  240 , the second platen  132  moves out of the ion beam path  102  and then the wafer on the first platen  130  moves into the ion beam path  102  immediately behind the wafer on the second platen  132  at steps  260  and  290 . A distance sufficient for preventing collisions due to mechanical, control and timing variations separates the two wafers as they pass through the ion beam path  102 . The wafer on the second platen  132  moves to the exchange position at step  260  simultaneous with the wafer on the first platen  130  being implanted at step  290 . The second exchanger  122  will exchange the processed wafer with an unprocessed wafer in the corresponding step  270 . The wafer on the second platen  132  and the corresponding second scan system  142  is moved to the pre-implant position at step  280  simultaneous with the ongoing wafer being implanted. These steps and processes are generally represented in FIGS.  1 ( e )- 1 ( g ).  
         [0016]     As the wafer on the first platen  130  completes the last implant pass at step  300 , the system controller  150  determines whether another cycle is to be repeated at step  310 . If another cycle is to be repeated, the wafer on the first platen  130  moves out of the ion beam path  102  and the wafer on the second platen  132  immediately moves into the ion beam path  102  at step  210  and  250 . Again, a distance sufficient for preventing collisions due to mechanical, control and timing variations separates the two wafers as they pass through the ion beam path  102 . The wafer on the first platen  130  returns to the wafer exchange position at step  210  simultaneous with the wafer on the second platen  132  being implanted at step  250 . The first exchanger  120  will exchange the processed wafer with an unprocessed wafer at the corresponding step  220 . This cycle continues until all wafers from the load lock  110  are processed and the system controller  150  determines that no other cycles are to be repeated at step  310 .  
         [0017]      FIG. 1 ( b ) illustrates the last implant pass of the first scan system  140  with the wafer on the first platen  130  as well as the first pass of the second scan system  142  with the wafer on the second platen  132 . The first and second platens  130  and  132  are controlled to minimize the clearance between the wafers on the respective platens to maximize utilization of the ion beam  102 .  FIG. 1 ( b ) generally corresponds to steps  210  and  250  in the flow chart of  FIG. 2 .  
         [0018]      FIG. 1 ( c ) illustrates the operation of the system according to the present embodiment after implanting of a first wafer is complete and the implanting of a second wafer is in process. The first exchanger  120  exchanges the processed wafer on the first platen  130  while the second wafer on the second platen  132  is implanted.  FIG. 1 ( c ) generally corresponds to steps  210 ,  220  and  250  in the flow chart of  FIG. 2 .  
         [0019]      FIG. 1 ( d ) illustrates a wafer on the second scan system  142  and the second platen  132  being implanted while the first scan system  140  and the first platen  130  move an unprocessed wafer to a pre-implant position.  FIG. 1 ( d ) generally corresponds to step  230  in the flow chart of  FIG. 2 .  
         [0020]      FIG. 1 ( e ) illustrates the last implant pass of a wafer by the second scan system  142  with the second platen  132  as well as the first pass of a wafer by the first scan system  140  with the first platen  130 . The first and second platens  130  and  132  are controlled to minimize the clearance between the wafers on the respective platens to maximize utilization of the ion beam  102 .  FIG. 1 ( e ) generally corresponds to steps  260  and  290  in the flow chart of  FIG. 2 .  
         [0021]      FIG. 1 ( f ) illustrates a wafer exchange by the exchanger  122  at the second platen  132  while the wafer on the first platen  130  of the first scan system  140  is being implanted.  FIG. 1 ( f ) generally corresponds to steps  260  and  290  in the flow chart of  FIG. 2 .  
         [0022]      FIG. 1 ( g ) illustrates the second scan system  142  with an unprocessed wafer on the second platen  132  in the pre-implant position.  FIG. 1 ( g ) generally corresponds to step  280  in the flow chart of  FIG. 2 . As indicated in the flow chart of  FIG. 2 , these steps will continue to repeat until all wafers are processed.  
         [0023]     Although the description above has been directed to a system including two wafer exchangers and two scan systems, it will be appreciated that the present invention may utilized any number of wafer transfer robots, scan systems and load locks. It may be advantageous to utilize two or more wafer transfer robots and scan systems to realize increased speed requirements so that wafers are continuously present to the beam. Such variations of the system described in FIGS.  1 ( a )- 1 ( g ) and  2  may be realized by one skilled in the art. Although the methods are systems have been described relative to specific embodiments thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, can be made by those skilled in the art. Accordingly, it will be understood that the present invention is not to be limited to the embodiments disclosed herein, can include practices otherwise than specifically described, and are to be interpreted as broadly as allowed under the law.