THE USE OF UPSTREAM AND DOWNSTREAM INFORMATION IN SCHEDULING SEMICONDUCTOR BATCH-OPERATIONS

This paper presents a control strategy that exploits and uses both upstream and downstream information on the current and expected states of a semiconductor manufacturing facility (FAB) to make intelligent batch size decisions. Through simulation, this strategy is compared with current methods that consider only upstream information, as well as with a general threshold policy. The results confirm that significant improvements in cycle time can be realized by exploiting upstream information. Some additional improvement can be gained at low to moderate traffic intensities by looking downstream. However, as traffic intensity increases, use of downstream information can actually lead to longer delays, indicating that the scheduling of the batch machine may be more important than the scheduling of the serial machine in congested systems.