A HIERARCHICAL APPROACH TO QUALIFICATION MANAGEMENT IN WAFER FABS

摘要

We discuss a qualification management problem arising in wafer fabs. The steppers need to be qualified to process lots of different families. A qualification time window is associated with each stepper and family. The time window can be reinitialized as needed and can be extended by on-time processing of lots from qualified families. In this paper, we propose a hierarchical approach for this problem. The base-level is a dispatching strategy that takes into account qualification decisions. The medial-level consists of a mixed integer linear programming formulation for making qualification decisions, whereas the top-level is a linear programming (LP) formulation that computes target quantities for the steppers for a planning window taking fab-wide objectives into account. We present results of simulation experiments where the hierarchical approach is applied in a rolling horizon manner. The results demonstrate that the LP-based approach outperforms a heuristic to determine target quantities.