New Scheduling Approach for Shared Resources and Mixed Storage Policies

We propose a new mixed-integer linear programming (MILP) model for scheduling automated wet-etching stations (AWS), which can be classified as a multistage batch plant with both zero-wait and local storage policies and featuring a robot for moving the wafer lots from one stage to the next. The novelty is the use of a slot-based approach for handling the processing tasks together with general precedence sequencing variables for dealing with the transportation tasks. The performance of the new continuous-time model is shown to be significantly better than a pure sequencing based formulation and a closely related hybrid model taken from the literature.