A Novel Vehicle Pre-dispatching Method for Automated Material Handling System in Semiconductor Manufacturing

As the demand for ultra-clean areas in semiconductor fabrication has increased, the need for more efficient automated material handling system (AMHS) has become imperative. A diffusion tool is characterized by its long processing time of 6-12 h, thus making it a form-batch manufacturing step. Out of necessity with this application, wafer lots are temporarily stored in stocker and are delivered to diffusion tools for processing when the Work-In-Process (WIP) level reaches 4-6 lots. As a result, diffusion tools wait for long wafer delivery time due to the current vehicle assignment method, thus greatly impacting transportation and production efficiency. In order to improve the transport performance, a novel vehicle assignment method is proposed. Unlike the current methods, which assign idle vehicles to move to load ports sequentially, the novel vehicle pre-dispatching method calls several idle vehicles to move to a load port to simultaneously execute transport jobs with the goal of shortening a vehicle's arrival time. To aid in our research, we performed simulation analysis of an AMHS for a diffusion area. The simulation outcome indicates that a substantial improvement in AMHS transport performance is achieved with applying of the vehicle pre-dispatching method.