Differentiated preemptive dispatching for automatic materials handling services in 300 mm semiconductor foundry

Highly automated materials handling in 300 mm semiconductor manufacturing is one of the biggest concerns to foundry practitioners because effective coordination among efficient manual operations has been the core competence in their 200 mm manufacturing successful stories. It is still very challenging to provide almost no-wait transport to hot lots (high priority lots) in an automatic materials handling production environment. This paper proposes an effective overhead hoist transport (OHT) dispatching rule, differentiated preemptive dispatching (DPD) policy, to reduce the possible blocking effects during the transportation of hot lots in a 300 mm OHT system. The dispatching objective is to minimize the delivery time of hot lots while minimizing the impact to the transport of normal lots. Simulation experiments based on realistic data from a local 300 mm foundry fab are conducted. Numerical results demonstrate that the DPD rule can effectively expedite the movements of hot lots. The proposed DPD rule is very useful to hot lots management and shop floor control functions, like scheduling and dispatching, in a 300 mm fab-wide automated production environment.