Multiple-objective real-time scheduler for semiconductor wafer fab using Colored Timed Object-oriented Petri nets (CTOPN)

This paper presents a multiple-objective real-time scheduler for semiconductor wafer fab using Colored Timed Object-oriented Petri net (CTOPN). First, a high-fidelity hierarchical CTOPN model of wafer fab is constructed, upon which a hierarchical control system is also formed. To rank WIP lots in meeting multiple scheduling objectives, a combined priority index is then developed in the fab level controller. To cope with unpredictable events occurred on the equipments, such as breakdown, real-time dispatching policies are encapsulated in the work station-level controllers, which dynamically dispatch wafer lot, and the dispatching results are fed back to fab controller through work area controllers.