The remaining time concept for dispatching on roller belt conveyor in 450-mm wafer fabrications

Abstract

Semiconductor industry is one of the most important industries in the world. One current trend of this industry is the increase of wafer size, from 300 to 450 mm, to improve throughput and lower cost. However, this change also brings challenge for 450-mm wafer fabs. One challenge is the difficulty of moving and handling the 450-mm wafers due to their increased size and weight. Another challenge is the need to prioritize lots in the shop floor so that hots can receive fast service to satisfy customer needs. Due to some specific advantages, the conveyor-based automated material handling system (AMHS) has been considered to be the next-generation transportation system for wafer transport in a 450-mm wafer fab. However, this kind of systems remains to have some problems, such as optimizing its performance, particularly with transport congestion. Hence, this study proposes a new heuristic preemptive dispatching method, termed remaining time algorithm (RTA), to operate an AMHS based on activated roller belt (ARB). In addition, the loop structure of the AMHS has been rearranged and some buffer components have been added into this AMHS. To investigate its effectiveness, the RTA has been compared to two previously proposed dispatching methods, the new heuristic preemptive dispatching belt (a-HPDB) in Wang et al. (Appl Sci 7:780, 2017) and the heuristic preemptive dispatching belt (HPDB) in Wang et al. (Comput Ind Eng 96:52–60, 2016). In terms of average lot delivery time, the simulation results show that for hot lots, the RTA is 1.38% and 8.77% better than the a-HPDB and HPDB, respectively; for normal lots, the RTA is 14.49% and 28.39% better than the a-HPDB and HPDB, respectively. Hence, the RTA is concluded being an effective dispatching method that can better deal with congestion problem, improve lot delivery time, and yield better system performance.