Abstract
This study investigates the transportation problems in the semiconductor fabrication. Due to the weight and size of the 300 mm wafer lot, it is difficult to transport lots by operators, and therefore the automated material handling system (AMHS) is widely employed. Nevertheless, in practice, there are several special situations where operators perform better than AMHS. To date, fully-automated transportation for an intrabay is still difficult to achieve, so that generally the hybrid transportation system (HTS) is adopted. Hence, this study focuses on the optimal design of the HTS that incorporate overhead hoist transports (OHTs) with operators. The proposed methodology exploits the colored timed Petri nets (CTPN) to model the HTS, which can be applied to diverse areas in the intrabay system of semiconductor fabrication, and the modeling tool for analyzing the HTS has to be generalized. The model structure is separated from the model configuration in modeling the HTS, and thus prevents the need to modify a model structure due to a different problem configuration. There are two sub-systems, the transportation system and the production system in the HTS. In the construction of the transportation system, one needs to consider simultaneously the different behavior of operators and OHTs, and different situations in the transportation.Also one needs to consider the different production behavior in the different fabrication areas. Then, these two sub-systems are combined and the CTPN-based hybrid transport system is transformed into a three-phase discrete event simulation system for further analysis. After simulating different scenarios, the response surface method (RSM) is used to obtain the optimal allocation of OHTs and operators. The results of this study can provide the needed information to support the decision for allocation of OHTs and operators. Besides, the CTPN-based HTS simulator is a general model which can be applied to diverse areas of semiconductor fabrication.