Reservation-based dispatching rule for make-to-order wafer FAB with high-priority lots

Abstract

Make-to-order wafer Fabrications (FABs) have to deal with two different types of lots: high priority and normal. High-priority lots have shorter cycle times, tighter target due dates, and higher margins than normal lots. This article presents a dispatching rule for on-time delivery of high-priority lots with low tardiness for normal lots. The proposed dispatching rule uses the concept of reservation, which refers to the provisional allocation of capacity for high-priority lots. The reservation policy has been applied to ensure capacity for high-priority lots in real FABs. The reservations of high-priority lots may cause considerable tardiness of normal lots. To cope with the problem, the proposed dispatching rule considers tool utilization as well as the on-time delivery of high-priority lots. Also, we introduce the concept of reservation depth to control the influence level of the reservation. The proposed dispatching rule has been implemented and outperforms conventional dispatching rules and conventional reservation policy.