Petri-net and GA based approach to modeling, scheduling, and performance evaluation for wafer fabrication

A significant amount of risk is involved in the wafer fabrication due to huge investment costs, long production cycle time, and short production life cycle. In this paper, a genetic algorithm (GA) embedded search strategy over a hybrid color-timed Petri-net (HCTPN) for wafer fabrication is proposed. Through the HCTPN model, all possible behaviors of the wafer manufacturing systems such as WIP status and machine status can be completely tracked down by the reachability graph of the net. The chromosome representation of the search nodes in GA is constructed directly from the HCTPN model, recording the information about the appropriate scheduling policy for each workstation in the fabrication. A better chromosome found by GA is received by the HCTPN based schedule builder, and then a near-optimal schedule is generated.