Development of a state-dependent dispatch rule using theory of constraints in near-real-world wafer fabrication

Wafer fabrication industries encounter challenging tasks to justify their performance among conflicting measures when making dispatch policy decisions. A state-dependent dispatch rule is developed to improve overall system performance, which consists of cycle time, work in process, throughput and due date performance. The theory of constraints is adopted as guiding principle to derive the state-dependent dispatch rule. Three state variables (machine utilization, machine queue length, and contention factor) and three dispatch rules (two boundary, shortest time to next visit, and fastest time for next visit) are considered to construct the dispatch rule. Response surface methodology is also applied to this study. A near-real-world fab model is developed to test the performance of the new rule. The simulation results show that the TOC-based state-dependent dispatch rule improves four performance measures simultaneously.