Systematic Construction and Performance Analysis of Cluster Tools Using Timed Petri Net Models

A cluster tool is an integrated, envi- ronmentally isolated manufacturing system consisting of process, transport, and cassette modules, mechan- ically linked together, that is used in manufacturing of semiconductor chips. Because of high throughput requirements, cluster tools perform a number of activ- ities concurrently. Petri nets are formal models devel- oped specifically for representation of concurrent ac- tivities and for their coordination. In timed nets, the durations of modeled activities are represented by oc- currence times associated with transitions, and this allows to study the performance characteristics of the modeled systems. Since cluster tools can be quite complex, a system- atic approach to generating net models is proposed. Net models derived in such a way have modular struc- ture, which is used to determine model’s steady–state performance on the basis of net invariants, without the exhaustive reachability analysis. Performance charac- teristics are obtained in symbolic form, in terms of modeling parameters, so different variants of cluster tools can be evaluated and compared very efficiently, without repetitive model analyses