Method for providing distributed material management and flow control in an integrated circuit factory

Abstract

A method for providing distributed material management and flow control in an integrated circuit (IC) factory. The IC factory comprises a factory stocker, a plurality of process bays and a factory transport agent for moving wafer cassettes between the bay and the stocker. Each of the bays comprises a bay stocker, a plurality of tools, a mini-stocker and a bay transport agent for moving wafers amongst the bay components. The apparatus uses partitioned stockers to facilitate deadlock avoidance or deadlock resolution. Additionally, various algorithms are used to detect wafer cassette movement situations where deadlocks may result from a wafer cassette movement within a bay and for resolving deadlocks when they occur.

1 . A method of moving wafer cassettes in an integrated-circuit factory comprising: 
 determining a target tool for a first wafer cassette;    determining whether a second wafer cassette is waiting for positioning in the target tool;    if the second wafer cassette is not waiting for positioning in the target tool, then moving the first wafer cassette into the target tool;    if the second wafer cassette is waiting, postponing the movement of the first wafer cassette into the target tool.    
   
   
       2 . The method of  claim 1  wherein the second wafer cassette that has been waiting longer for entry into the target tool has a higher priority for entry to the target tool than the first wafer cassette.  
   
   
       3 . The method of  claim 1  further comprising: 
 determining a capacity of cassettes for a process bay loop serving the target tool; and    adding the first cassette to the loop if the capacity of the loop exceeds a number of cassettes present in the loop by two.    
   
   
       4 . The method of  claim 3  further comprising: 
 identifying a condition whenever there are N−1 cassettes present in the loop, and wherein the loop has a capacity of N cassettes.    
   
   
       5 . The method of  claim 1  further comprising: 
 identifying a knot tool in a process bay loop which serves the target tool.    
   
   
       6 . The method of  claim 5  further comprising: 
 checking the knot tool for a deadlock condition prior to assignment of the first wafer cassette.    
   
   
       7 . The method of  claim 6 , wherein the deadlock condition for the knot tool exists whenever there are N−1 cassettes present in the loop, and wherein the loop as a capacity of N cassettes.  
   
   
       8 . A method of detecting deadlocks in an integrated-circuit factory comprising: 
 a) initialize a variable to a first location in a semiconductor wafer processing system;    b) determining a successor location to the first location;    c) determining if the successor location for a wafer cassette is empty or is a stocker, then a deadlock is not detected; if the successor location for a cassette is not empty or a stocker and the successor location is a location already identified in a schedule, then identify the existence of a circular wait;    d) save the first location in a schedule;    e) equate the first location equal the successor location;    f) repeat steps b), c), d), e) and f) until all successor locations are found.    
   
   
       9 . A method for providing stocker overflow protection in an integrated-circuit factory comprising: 
 sending a transfer request from a first stocker to a second stocker, where said transfer request comprises a window size defining a number of wafer cassettes that the first stocker desires to send to the second stocker;    comparing the window size to the available space in the second stocker;    if the window size is greater than the available space in second stocker, rejecting the transfer request; and    if the window size is less than or equal to the available space in the second stocker, accepting the transfer request and transferring said number of wafer cassettes from the first stocker to the second stocker.    
   
   
       10 . The method of  claim 9  further comprising updating a status database in said first stocker and second stocker to reflect the transfer of the number of wafer cassettes.