Vehicle OHT Dispatching Performance Analysis of an AMHS in 300 mm Semiconductor FABs

To improve the performance of an automated material handling system （AMHS） in 300 mm semiconductor fabrication plants （ FABs ）, an overhead-hoist-transport （ OHT ） vehicle dispatching problem was described for semiconductor FABs. An original wafer lot dispatching policy was proposed. To minimize costs due to transportation logic, a dispatching rule based on an adapted Hungarian algorithm was presented, and six factors were considered. In addition to the recurring parameters, two original parameters of the vehicles utilization and wafer lot priority were considered to evaluate system performance. To obtain a balanced efficiency regarding the FAB output factors, simulation and sensitive analysis were used to find the best weight parameters of the cost matrix. In particular, a high rate of priority wafer lots （ greater than 20 % ） and vehicles utilization （ greater than 75 % ） are obtained without penalizing the efficiency of the FABs. The results indicate that the proposed dispatching policy is valid and practical.