The heuristic preemptive dispatching rule using stocker for conveyor-based material handling system of 450-mm wafer fabrication

Abstract

Transition from 300 to 450 mm wafer fabrication is the current trend in the semiconductor industry due to the benefits of higher productivity and lower production cost. However, the increased size and weight of 450 mm wafers will cause handling and transport problems, which prompts the need of an effective and capable automated material handling system (AMHS). Some researchers have proposed using conveyor-based AMHS as the next-generation transport means for 450 mm wafer fabrication. However, the lack of effective dispatching rules will make a conveyor-based AMHS to remain suffering traffic-jam problems and unable to prioritize lots to meet customer needs. In this research, a dispatching rule called “heuristic preemptive dispatching rule using stocker (HPDS)” is proposed to control wafer movements in a conveyor-based AMHS for 450-mm wafer fabrication. Simulation has been conducted and the results showed the HPDS outperformed the differentiated preemptive dispatching (DPD) in terms of average variable time that includes block and waiting times.