This paper addresses the problem of controlling the Work-In-Process (WIP) in semiconductor manufacturing by using a global scheduling approach and manufacturing scheduling software. A WIP balancing strategy is proposed to minimize the product mix variability in terms of throughput and cycle time. This strategy is enforced using a global scheduling optimization model which is formulated as a linear programming model. The global scheduling model is coupled with a generic multi-method simulation model built with manufacturing scheduling software for evaluation purpose.
Using manufacturing scheduling software, different strategies can be implemented in the global scheduling approach depending on the KPIs that the fab (Front-End manufacturing facilitiy) manager wants to optimize. In this paper, the strategy is enforced using a global scheduling model written as a linear programming model. Its objective function embeds some Work-In-Process management goals such as the minimization of the remaining WIP in each operation and a Work-In-Process balancing control. The fab simulation model helps to evaluate the impact of our global scheduling approach. In this model, the First-In-First-Out (FIFO) dispatching rule is used in work-centers, combined with a rule to ensure that global scheduling production targets are followed.
The simulation model, coded with the AnyLogic as manufacturing scheduling software, is a multi-method simulation model which combines Discrete Event (DE) and Agent Based (AB) simulation methods. The notion of queues in Discrete-Event Simulation is used and the flexibility, behavior, and communication of agents is used in Agent Based simulation. The main types of agents are the lots and the work-centers. Secondary agents are non-physical components such as operations and routes. For more information on the data driven generic multi-method simulation model, see
Global scheduling approach