A PLANNER AND SCHEDULER FOR SEMICONDUCTOR MANUFACTURING

The Microelectronics Manufacturing Science & Technology (MMST) project includes two closely related CIM subsystems for planning and scheduling wafer production. The MMST Planner plans all work release into a factory so as to meet stated goals, and predicts work completion dates. The MMST Scheduler operates in real-time to determine the sequence of lot movements and machine loadings that will be performed on the fab floor. Both the Planner and the Scheduler continually maintain plans which are up to date with the factory status by incrementally replanning for unexpected events. The MMST Planner can be used as a decision support tool to rapidly analyze the consequences of various manufacturing decisions. Planning is performed using a modified beam search algorithm, and is based on a time-phased capacity model of the factory. Fuzzy arithmetic is used to model the uncertainty inherent in cycle time data. The MMST Planner is fully distributed, allowing simultaneous users in different parts of the factory. The MMST Scheduler uses a heuristic method called Score Tables to develop schedules of future events. The Scheduler evaluates event prerequisites to determine when to initiate lot transfers and machine loadings, and responds to any failures of execution.