Optimizing the Allocation of Single-Lot Stockers in an AMHS in Semiconductor Manufacturing

This paper addresses the problem of optimally allocating single-lot stockers, also called bins, to machines in an Automated Material Handling System (AMHS) of a semiconductor wafer manufacturing facility. A Mixed Integer Linear Programming (MILP) model is proposed that assigns single-lot stockers to groups of machines performing the same types of operations. Two criteria are minimized: The maximum travel time from bins to machines and the maximum utilization of bins. An important characteristic of the problem is that the number of changes from the original allocation is limited. Computational experimental on industrial data with more than 2,000 bins and 40 machine groups are conducted. The solutions of the MILP are analyzed with regard to the trade-off between the two criteria and the impact of the allowed number of changes.