Flow Line Models for hightech manufacturing: theory, application and optimization

Abstract

Flow lines have been studied for many years as models of manufacturing systems and they are par-ticularly appropriate for the modeling in high-tech manufacturing. They can provide very accurate perfor-mance estimates and are thus good candidates for use as models in various manufacturing industries. To develop understanding and intuitions for behaviors of such flow lines, we conduct theoretical studies. For deterministic hybrid flow lines with single customer class, we use the max-plus algebra to obtain an upper bound for the customer completion times which requires less computation than full flow line simulation. For deterministic hybrid flow lines with multiple classes of customer and no overtaking, we also develop upper bounds on the customer completion times. For this general class of systems, the bounds are the most that one can deduce; examples can be constructed where equality is achieved and where it is not. We incorporate a very general class of setups and similarly obtain upper bounds. Motivated by real manufacturing systems, we use such flow line models into two applications; fab-level simulation models and release scheduling in a tool. First, we develop models for clustered photolithography tools (CPTs) for use in fab-level simulation. Simulation models are often employed to support decision making in semiconductor wafer manufacturing by helping to assess the cycle time and throughput implications of various changes to the system. An essential element of creating such a simulation is the selection of the appropriate level of detail for the model. While detailed models are more expressive and may provide high accuracy, they carry twin burdens of modeling complexity and computational intractability. In an effort to more deeply understand the nature of the tradeoff between fidelity and complexity for CPT models, we study the character of equipment models rang-ing from linear to flow line. With knowledge inspired by flow lines, we develop extensions ...