The aim of this paper is to present the rationale, a numerical example and a case study of the application of an algorithm to convert non‐calendar based preventive maintenance (PM) schedules into calendar‐time format for semiconductor manufacturing systems (SMS). The resulting calendar‐time PM schedules can be utilized as a baseline within a PM scheduling optimization process.
The algorithm utilizes estimations of work‐in‐process (WIP) and system parameters to estimate an equivalent calendar‐time schedule for PM schedules based on different units. A numerical example based on fictitious data illustrates the utilization of the conversion algorithm within a mixed PM scheduling scenario, including wafer, processing‐time and energy‐based PM tasks for multi‐chamber tools. In addition, a case study illustrates the accuracy of the algorithm by comparing estimated PM targets (i.e. due, warning and late dates) with historical data from a real semiconductor fabrication facility.
Results from the case study validated the conversion algorithm by showing accurate estimations of PM targets (i.e. due, warning and late dates). The accuracy of the algorithm depends, however, on good estimates for WIP levels within the planning horizon.
The conversion algorithm may be utilized not only in SMS but also in other industries that require the conversion of non‐calendar based PM schedules into calendar‐time format for PM optimization and operational purposes.
