Abstract:
An wafer positioning system comprises a wafer handling chamber with a vacuum sealable opening catching wafers. At least one processing chamber disposed adjacent to the wafer handling chamber has an opening catching wafers, sealed with a gate. A wafer transfer robot with a tray disposed in the wafer handling chamber transports wafers into the processing chambers. A signal receiver is disposed on the front end of the tray. When the tray passes below a wafer, the signal receiver detects wafer position, generating a wafer position signal. A control module receives the wafer position signal through the signal receiver and compares the wafer position signal with a predetermined position signal to correct any misalignment of the wafer.

Description:
BACKGROUND  
       [0001]     The invention relates to wafer positioning systems, and in particular to an on-line wafer positioning system having signal receiver to detect wafer position.  
         [0002]     Semiconductor manufacturing processes include processes such as oxidation, diffusion, lithography, etching, CVD, and others. To integrate related processes in a single system and process and transfer wafers quickly in a vacuum environment avoiding contamination, automatic semiconductor manufacturing equipment is critical.  
         [0003]     Multi-process chambers require less space, have a shortened production period, and consume less vacuum system resources. A general multi-process chamber design, as shown in  FIG. 1 , comprises a front end wafer handling chamber  14  connecting the transfer system of the factory and transferring wafer carriers to a load lock chamber  16  via robots  18 . Further, a wafer handling chamber  20  is disposed in the center of the machine, in which a wafer transfer apparatus  22  is disposed and further comprises a wafer transfer robot  28 . Outside the wafer handling chamber  20 , a plurality of processing chambers  24  and cooling chambers  25  are disposed to load/unload wafers. The wafer transfer robot  28  is controlled by optical detection through a position point  32  of a position stage  34  (only partially shown). Moreover, through the wafer transfer robot  28 , wafers  30  can be moved from the load lock chamber  16  to the processing chambers  24  to execute various processes or from the processing chambers  24  to the cooling chambers  25  to be cooled.  
         [0004]     Wafers  30  are supported by a tray  26  and move between processing chambers  24  by the wafer transfer robot  28  in the wafer handling chamber  20 . Due to mechanical loss, the wafer transfer robot  28 , however, may cause displacement of the wafer position and is incapable of accurate, wafer positioning in the processing chambers. Such displacement may create process instability and malfunction of the vacuum clamp head. Due to the vacuum state of the wafer handling chamber, the machine must stop product processing and break vacuum to conduct the maintenance, interrupting production and possibly damaging wafers. Furthermore, if horizontally mis-positioned, the wafer transfer robot  28  may lose horizontal stability, thus generating vibration, further damaging wafers and the wafer carrier.  
         [0005]     U.S. Pat. No. 6,275,297 discloses a system and method of wafer position detection on a wafer transfer robot. A transparent area is disposed above the transfer channel between the wafer handling chamber and the processing chamber. Utilizing an optical sensor and a reflective device disposed on the wafer transfer robot to determine the distance between the wafer and the edge of the tray of the wafer transfer robot, wafer position accuracy can be determined. In a conventional system, however, only relative wafer position can be detected. Further, it is impossible to determine whether the abnormality is a result of mechanical loss or simple mis-positioning. Thus, when the control unit corrects the movement of the wafer transfer robot in accordance with the bias of the wafer position, wafers can still be mis-positioned due to inaccurate correction of the wafer transfer robot.  
       SUMMARY  
       [0006]     An wafer positioning system comprises a wafer handling chamber with a vacuum sealable opening catching wafers. At least one processing chamber disposed adjacent to the wafer handling chamber has an opening catching wafers, sealed with a gate. A wafer transfer robot with a tray disposed in the wafer handling chamber transports wafers into the processing chambers. A signal receiver is disposed on the front end of the tray. When the tray passes below a wafer, the signal receiver detects wafer position, generating a wafer position signal. A control module receives the wafer position signal through the signal receiver and compares the wafer position signal with a predetermined position signal to correct any misalignment of the wafer. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0007]     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a diagram of a conventional multi-process chamber;  
         [0009]      FIG. 2A  is a diagram of a wafer positioning system;  
         [0010]      FIG. 2B  is a diagram of a wafer transfer robot of the system described in  FIG. 2A  catching a wafer;  
         [0011]      FIG. 3A  is a top view of a wafer transfer robot, catching a wafer, of the wafer positioning system;  
         [0012]      FIG. 3B  is a side view of a wafer transfer robot, catching a wafer, of the wafer positioning system;  
         [0013]      FIG. 4  is a diagram of the position signal of the signal receiver of the wafer positioning system; and  
         [0014]      FIG. 5  is a flowchart of a wafer positioning method. 
     
    
     DETAILED DESCRIPTION  
       [0015]      FIG. 2A  is a diagram of a wafer positioning system and  FIG. 2B  shows a wafer transfer robot thereof catching a wafer. To simplify figures, a multi-process chamber  50  is shown in  FIG. 2A  &amp;  FIG. 2B  without the front end wafer handling chamber and the wafer transfer robot in  FIG. 1 .  
         [0016]     As shown in  FIG. 2A  &amp;  FIG. 2B , a multi-process chamber  50  comprises a wafer handling chamber  56  connected to the exterior via a vacuum chamber  54 , sealed by a shutter  541 . Outside the wafer handling chamber  56 , a plurality of processing chambers  60  and cooling chambers  62  are disposed, each comprising a passage  601  and a gate  602 . A wafer  30  enters the processing chamber  60  through the passage  601  and the gate  602  closes the passage  601 . A wafer transfer robot  58 , disposed to deliver the wafer  30 , comprises a sub robot  581 , a connection portion  582 , and a tray  584  bearing the wafer  30 . A control module  52  controls the system, e.g. the movement of the wafer transfer robot  58  and the process parameters of the processing chamber. Additionally, in this embodiment of the multi-process chamber  50 , a plurality of planar mirrors  64  are disposed above the passage  601 , connecting the wafer handling chamber  56 , the processing chamber  60 , the cooling chambers  62 , and the vacuum chamber  54 , to calibrate the transfer system.  
         [0017]     As shown in  FIG. 2A , when the wafer  30  possess a process such as dry etching, CVD, or RTP, and the gate  602  is open, the wafer transfer robot  58  aligns with the processing chamber  60 , in preparation to remove the wafer  30 . As shown in  FIG. 2B , when moving from the retracted state to the processing chamber  60 , the wafer transfer robot  58  sequentially passes below the planar mirror  64 , the passage  601 , and the wafer  30 . When the tray  584  is positioned, an apparatus (not shown) introduced to support the wafer  30  inside the processing chamber  60  withdraws to stably seat the wafer  30  on the tray  584 . The wafer transfer robot  58  retracts and prepares to deliver the wafer  30  to the next processing chamber  60  or target.  
         [0018]     The multi-process machine  50  of the invention provides wafer positioning by disposing a signal emitter and a signal receiver on the front end, whereby when the tray  584  passes below the planar mirror  64  and the wafer  30 , the signal receiver receives light from the signal emitter reflected by the planar mirrors  64  and the wafer  30 , forming two position signals. The control module  52  compares these signals with the predetermined position signals to determine whether the wafer  30  is accurately positioned.  
         [0019]     The mentioned signal emitter and signal receiver as disclosed are preferably reflective fiber sensors  66  such as Keyence FS-V20 or FU-32. Referring to  FIG. 3A  &amp;  FIG. 3B , the fibers of the two reflective fiber sensors  66  can be disposed along the edge of the tray  584  of the wafer transfer robot  58 . The emitter  68  of the sensor is fixed on both sides of the front end of the tray  584  and the emitter  68  emits a predetermined wavelength upward. When the wafer transfer robot  58  enters the processing chamber, the tray  584  sequentially passes below the planar mirror  64  and the wafer  30 , and the reflective fiber sensor  66  receives the light reflected by the planar mirrors  64  and the wafer  30 , enabling light intensity of the sensor  66  to change. Further, by comparing the predetermined position signal and the received position signal, the control module  52  determines whether the wafer transfer robot  58  is operating properly and whether the wafer  30  is normally positioned. To increase light intensity of the reflective fiber sensor, as shown in  FIG. 3A , the planar mirror  64  comprises two rectangular holes  641 ,  642  of different widths, sequentially disposed.  
         [0020]      FIG. 4  is a diagram of the position signal of the signal receiver of the wafer positioning system. Referring to  FIG. 3B  &amp;  FIG. 4 , the control module  52  of the invention comprises a predetermined calibration signal  71  and a predetermined position signal  72  measured from normal operation of the wafer transfer robot  58 . When the wafer  30  located in the processing chamber is mis-positioned and the wafer transfer robot  58  is operating normally, the predetermined calibration signal  71  and the calibration signal  73  received by the reflective fiber sensor  66  will be consistent, but the wafer position signal  74  will experience a position shift from the predetermined position signal  72 . Additionally, the control module  52  can calculate the accurate planar position of the wafer  30  through the wafer position signal  74  measured by two reflective fiber sensors  66 , further determining the position shift between the wafer  30  and the tray  584 . Thus, the control module  52  can correct successive movements of the wafer transfer robot  58  in accordance with the position shift and control the wafer transfer robot  58  to precisely deliver the wafer  30  to the next position.  
         [0021]     When the wafer transfer robot  58  is not normally positioned due to mechanical or other malfunction, as shown in Rn of  FIG. 4 , the calibration signal  75  experiences a position shift from the predetermined calibration signal  71 . If the position shift is beyond an allowable range, the wafer transfer robot  58  is determined to be abnormal and the system is stopped processing and recalibrated to avoid damage to wafer  30  or other apparatus.  
         [0022]      FIG. 5  is a flowchart of a wafer positioning method. In a wafer positioning method of the invention, a predetermined position signal  72  and a predetermined calibration signal  71  are provided after calibrating the system (S 501 ). Under normal operation, the wafer transfer robot  58  delivers the wafer  30  to the processing chamber  60 . When processing is complete, the wafer transfer robot  58  extends to the processing chamber  60 , removing the wafer  30 , and when the tray  584  passes below the planar mirror  64 , a signal receiver  66  measures the position of the planar mirror  64 , generating a calibration signal (S 502 ). Control module  52  further compares the calibration signal with the predetermined calibration signal (S 503 ) and if the calibration signal is not consistent with the predetermined calibration signal and beyond an allowable range, the control module  52  sends an alarm message and stops both the operation of the wafer transfer robot  58  and the system (S 504 ). If the calibration signal is consistent with the predetermined calibration signal, the wafer transfer robot  58  is operating normally. When the tray  584  passes below the wafer  30 , the signal receiver  66  measures the position of the wafer  30 , generating a wafer position signal (S 505 ). The control module  52  compares the wafer position signal with the predetermined position signal (S 506 ). If the wafer position signal is consistent with the predetermined position signal  72 , the control module  52  does not correct the movement of the wafer transfer robot  58  and directly processes the next target position and repeats the cycle (S 509 ). If the wafer position signal is inconsistent with the predetermined position signal  72 , the control module  52  determines a position shift of the wafer  30  in accordance with the wafer position signal (S 507 ) and corrects the next movement of the wafer transfer robot  58  in accordance with the position shift (S 508 ). The wafer transfer robot  58  precisely delivers the wafer  30  to the position of next processing chamber  60  (S 509 ).  
         [0023]     The wafer positioning system of the invention utilizes a signal receiver disposed on the front end of the wafer transfer robot. Additionally, the control module obtains information on the wafer transfer robot in the wafer handling chamber, determining whether the wafer position is accurate. If the wafer position is abnormal, the control module corrects the transfer movement of the wafer to maintain the wafer in the required position without stopping product processing and breaking the vacuum for maintenance. Thus, maintenance time of the machine is extended.  
         [0024]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.