Planning Wafer Starts Using Nonlinear Clearing Functions: A Large-Scale Experiment

Abstract

The nonlinear, circular dependency between workload and cycle times for production resources governed by queueing behavior has been a longstanding difficulty in the production planning domain. The issue is particularly important for semiconductor wafer fabrication facilities, which must operate at relatively high utilization to be profitable. Nonlinear clearing functions that relate the expected output of a resource in a planning period to the amount of work available to it have been proposed as an alternative approach. While computational tests on small systems have been promising, the question of whether the results remain valid for large-scale systems has remained open. In this paper we evaluate the performance of a clearing function based production planning model using a simulation of a large-scale wafer fab with two products and several hundred operations. Results indicate that, consistent with the results of previous experiments, the clearing function model yields substantial improvements in profit over conventional linear programming models.