Real time scheduler for wafer foundry fab with Object-oriented Petri nets

This paper presents the scheme of a multiple-objective real-time scheduler for semiconductor wafer fab using Colored Timed Object-oriented Petri nets (CTOPN). First, a high-fidelity hierarchical CTOPN model of the 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 lost, and the dispatching results are fed back to fab controller through work area controllers.