Production Planning and WIP Assignment for Wafer Fabrication Tools With Availability Constraints

This paper deals with a short-term production plan of a single toolset during a shift at a semiconductor fabrication plant. We propose a cost-based optimization model that seeks to minimize the cost of the shift while meeting the following conditions: 1) the shift produces its required output, measured in work-in-process (WIP) levels; 2) preventive maintenance (PM) tasks are carried out in compliance with the manufacturer´s recommended PM policy; and 3) the equipment undergoes cleaning operations, as recommended by the manufacturer, in a way that minimizes the production of blank wafers (a by-product of the cleaning process). A linear programming model is formulated and a practical procedure is provided to solve this production plan problem. Data from a real fab are used to demonstrate the optimality and applicability of the proposed approach. Results of various sensitivity analyzes further demonstrate how the model can be used to analyze the impact of changes in cost parameters, WIP levels and production rate parameters on the optimal solution.