Patent Publication Number: US-2004054543-A1

Title: Storage and management method for a multi-floor stocker system

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to a storage and management method for a multi-floor stocker system, which combines push and pull functions and table-oriented delivery management to optimally distribute lots of work-in-process (WIP) to all stockers in the multi-floor system, thereby effectively utilizing every stocker.  
       [0003] 2. Description of the Related Art  
       [0004] Currently, automated storage/retrieval is a must in wafer industries. For a wafer processing manufacturer, multi-floor stocker structure is widely employed in automated storage/retrieval to save required space and increase managing efficiency for WIP. Configuration of equipment and production flow usually collects identical or similar machine(s) in the same tunnel. Thus, multiple tunnels with different processing equipment are formed. A rail-guided vehicle (RGV) is implemented between tunnels to shuttle loads such as WIP between tunnels for processes such as lithography, etching, diffusion, and film thin processing. However, due to many factors, such as different process time and equipment number, a certain number of WIPs may not be processed as soon arriving at their destination or being shuttled to the next destination after processing. Accordingly, a stocker system is important, especially a multi-floor stocker system for a modern building, to gain the best operation efficiency on very expensive wafer processing equipment. Unfortunately, a storage and management method complying with the multi-floor stocker system has not been provided without additional stocker equipment.  
       SUMMARY OF THE INVENTION  
       [0005] Therefore, an object of the invention is to provide a storage and management method for a multi-floor stocker system, which combines push and pull stocking and a table-oriented management scheme to optimally distribute work-in-process (WIP) in the multi-floor stocker system.  
       [0006] Accordingly, the storage and management method for a multi-floor stocker system includes the following steps: checking storage capacities of all floors when a request from a desired lot is received; performing a pull function on the desired lot by a computer command or by hand if the desired lot will be delivered in/out a floor without sufficient storage capacity; and otherwise performing a push function for storing the desired lot according to a predetermined from-to table. The method further includes the steps of determining if a request of an undesired lot comes from a dummy lot or a monitor lot; storing the undesired lot to a preset shelter if the request comes from a dummy lot or a monitor lot; determining if the undesired lot has an assignment on the same floor if the request does not come from a dummy lot or a monitor lot; delivering the undesired lot according to the assignment on the same floor; and otherwise, delivering the undesired lot to a floor with sufficient storage capacity using the push function according to the from-to table. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007]FIG. 1 is a schematic diagram of a multi-floor stocker system according to the invention;  
     [0008]FIG. 2 is a flowchart of a storage and management method complying with the multi-floor stocker system in FIG. 1 according to the invention;  
     [0009]FIG. 3 is a flowchart of a pull function according to the invention;  
     [0010]FIG. 4 is a flowchart of a push function according to the invention;  
     [0011]FIG. 5 is a flowchart of a from-to table establishment method according to the invention;  
     [0012]FIG. 6 is an example of an evaluation table for every product; and  
     [0013]FIG. 7 is an example of the from-to table. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0014] The following similar function elements are denoted by the same reference numerals.  
     [0015]FIG. 1 shows a schematic diagram of a multi-floor stocker system  10  according to the invention. For simple description, FIG. 1 only shows two ports such as P 13 , P 31  or P 23 , P 32  and a robot for each floor (such as stocker i  or stocker i+1 ) and an I/O port such as IO 11  or IO 13  for two adjacent floors (such as stocker i  and stocker i+1 ). The ports P 13 , P 31 , P 23 , and P 32  are used for lot attachment/detachment and the ports IO 11  and IO 13  are used for lot storage/retrieval. The robot is responsible from processing a desired lot for any action controlled by a computer with predetermined programming (control logic).  
     [0016]FIG. 2 is a flowchart of a storage and management method complying with the multi-floor stocker system in FIG. 1 according to the invention. As shown in FIG. 2, an auto-delivery system is not always more effective than a manual system, especially in a small factory. For this, in step S 1 , first determine if a request for delivering and storing a WIP belongs to a desired lot. Next, step S 2  further determines if storage capacity for the desired lot is sufficient. Next, in step S 3 , a push function is performed, according to a predetermined from-to table, to store the desired lot to a stocker in the same or different floor with sufficient storage capacity. Also, in step S 4 , a pull function is performed by a computer or by hand in order to pull the lot in/out if the request is not from the desired lot (i.e. an undesired lot, which can include dummy lot, monitor lot and hold lot) or the desired lot has been forwarded to a floor without sufficient storage capacity. As cited above, the pull function, the push function and the from-to table are further described in the following drawings.  
     [0017]FIG. 3 is a flowchart of the pull function according to the invention. As shown in FIG. 3, floors FL i  and FL i+1  are subsequent. The floor FL i  has a process station Step i  and a stocker Stocker i . The floor FL i+1  has a process station Step i+1  and a stocker Stocker i+1 . In the pull function, after a desired lot is stored in a stocker and a material control system (not shown) records the address, the storage action is completed. When the lot is not stored in a suitable stocker and has to be moved to another stocker, this can be achieved by receiving a move command from an operator at Stocker i  (step  1 ) or a job prepare preset in a host&#39;s GUI (step  2 ). Thus, a workstation ws can give a command to the floor FL i  (step  3 ) to forward the desired lot to Stocker i+1  (step  4 ). The movement is not automatically completed but is performed only when receiving further instruction. The further instruction is: (1) using a job prepare instruction to forward the desired lot to a destination stocker through an attachment/detachment port and a storage/retrieval port if a desired lot is located in the same process station, and (2) using a move command and assigning a process to store or forward the desired lot to a destination stocker if the desired lot is not located in the same process station.  
     [0018]FIG. 4 is a flowchart of the push function according to the invention. As shown in FIG. 4, the main configuration is similar to that of FIG. 3 except for use of the GUI. Instead of a GUI, the push function uses a predetermined from-to table to automatically correct job preparation as need. Thus, when the process station Step i  sends a request to the workstation WS (step  1 ), the workstation WS can directly give an appropriate instruction with reference to the preinstalled from-to table (step  2 ). The process station Step i  moves a desired lot from Stocker i  to Stocker i+1  (step  3 ) or other processes according to the instruction. As cited above, the design of the from-to table is a key point for the performance efficiency.  
     [0019]FIG. 5 is a flowchart of a from-to table establishment method according to the invention. As shown in FIG. 5, the from-to table establishment includes three steps: evaluation of a step process time and a step equipment number (S 1 ); calculation of a step work ability for every stage based on the step process time and step equipment number of every product (s 2 ); and summary of the step work ability for every stage and production of a from-to table (S 3 ).  
     [0020] For evaluation of the step process time and the step equipment number, table  1  is given in FIG. 6. In FIG. 6, a product P 1  has five operations O 1 -O 5 , five recipes R 1,1 -R 1,5  and five capabilities C 1,1 -C 1,5  with respect to five stages S 1,1 -S 1,5 . A product P 2  has four operations O 1 -O 4 , four recipes R 1,1 -R 1,4  and four capabilities C 1,1 -C 1,4  with respect to four stages S 1,1 -S 1,4 . Every stage has different equipment numbers. For example, in this case, there are totally seven equipment numbers E 1 -E 7 : E 1 -E 3  respectively for S 1,1 , S 1,4  and S 2,1 ; E 4  respectively for S 1,2  and S 2,2 ; E 1 , E 5  respectively for S 1,3  and S 2,3 ; E 6 , E 7  for S 1,5 ; and E 2 , E 3  for S 2,4 . Equipment in each stage can respond to a process time and a channel. For example, in this case, equipment E 1  in stage S 1,1 , corresponds to a process time P 1,1,1  and a channel T 1  while equipment E 1  in stage S 1,3  corresponds to a process time P 1,1,2  and the channel T 1 . The process time P 1,1,1  denotes a first process time of E 1  for P 1  and the process time P 1,1,2  denotes a second process time of E 1  for P 1 . Likewise, process time P 2,4,1  denotes a first process time of E 4  for P 2  and the remaining are the like. The step process time is defined as the step process time per channel-per operation and evaluated by taking an average for every channel. For example, in channel T 1 , step process time AP 1,1,1  equals the average of P 1,1,1  and P 1,2,1 . Moreover, in channel T 2 , step process time AP 1,1,2  equals the average of P 1,3,1 . The remaining step process time is the same. Additionally, equipment can be used at different stages for a product. For example, for P 1 , E 1  is used at operations O 1,1 , O 1,3 , O 1,4  and E 2  is used at operations O 1,1 , O 1,4 . Thus, for each operation in P 1 , the utility probability is {fraction (1/3)} for E 1  and {fraction (1/2)} for E 2 . The equipment Id number defining the real equipment number used by per stage-per product is product mix PM 1  multiplying ({fraction (1/3)}) for E 1  and product mix PM 1  multiplied by {fraction (1/2)} for E 2 . PM 1  is the ratio of the amount of P 1  to the total amount of all products. Likewise, PM 2  is the ratio of the amount of P 2  to the total amount of all products. In this case, therefore, PM 1 +PM 2 =1. However, it can be more than two products. As such, the sum of all product mixes should be 1. The step equipment number such as N 1,1,1  is PM 1  multiplying (⅓+½). The remaining step equipment numbers are obtained in the same manner. The result evaluated for the step process time and the step equipment number is listed in a table as shown in FIG. 6. Accordingly, step work ability can be calculated by taking the ratio of step process time to step equipment number in each channel (S 2  in FIG. 5) and the step work ability for every stage is summarized in a table (S 3  in FIG. 5).  
     [0021] Therefore, a from-to table as shown in FIG. 7 is established. In FIG. 7, the value of step work ability becomes low with high work ability and high turn rate. High turn rate means less WIP to be stacked. With reference to the from-to table, when an operation on a desired lot is completed and the desired lot is stored in a stocker, the system sends the desired lot to an assigned stocker according to its stage and capability of next operation. A tunnel corresponds to the stocker (stocker Id) most convenient for storage/retrieval. Because the same or similar functional equipment may be disposed in different tunnels or even different floors, a stage and capability may be mapped to more than one stocker, for example, (S* 1 , C* 1,1 ) to (STK 1 , STK 2 ) and (S* 4 , C* 4,1 ) to (STK 1 , STK 2 ). An example of determination to store the desired lot in STK 1  or STK 2  is given under the condition of S* 1  and C* 1,1 . If WIP* i  is the current WIP amount in STK i , and W* i  is the work ability of STK i , and STK 1  is a default stocker, wherein i is 1 or 2, the delivery logic is:  
     [0022] If (WIP* 1 /W* 1 ) (WIP* 2 /W* 2 ), the desired lot is sent to STK 1 .  
     [0023] If (WIP* 1 /W* 1 )&gt;(WIP* 2 /W* 2 ), the desired lot is sent to STK 2 .  
     [0024] Further, a high water mark (HWM) is used to preserve a buffer region in a stocker to buffer a processed lot to be forwarded to next operation or to indicate a desired lot to be processed temporarily stored to an alternate stocker until a low water mark (LWM) is signaled to release the HWM. When the HWM is released by the LWM, the desired lot to be processed is sent back from the alternate stocker to the stocker and operated as usual.  
     [0025] To summarize above, the invention provides a storage and management method for a multi-floor stocker system, which combines push and pull function and a from-to table to optimally distribute lots of work-in-process (WIP) to all stockers in the multi-floor system, thereby effectively utilizing every stocker.  
     [0026] Although the invention has been described in its preferred embodiment, it is not intended to limit the invention to the precise embodiment disclosed herein. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.