Simulation based real-time scheduling in a semiconductor wafer fabrication facility

Abstract

This paper presents a real-time scheduling methodology in a semiconductor wafer fab that produces multiple-type products with different due dates and different process flows for the objective of minimizing total tardiness of orders for the products. In the wafer fab, wafer lots are processed on serial processing and batch processing workstations, each of which consists of parallel identical machines. In the suggested real-time scheduler, which uses simulation and priority rules, lot scheduling rules and batch scheduling rules are selected from sets of candidate rules based on information obtained from discrete event simulation. Since rule combination that gives the best performance may vary according to the status of the fab, in the real-time scheduler a number of rule combinations are tested in a dynamic situation and the best is selected and employed for a certain period of time. Various strategies that can be used in such a simulation-based real-time scheduling method are tested through computational experiments on a number of test problems.