The automated material handling system (AMHS) may become a critical factor that constrains the capacity of 12-wafer-lot systems. In this paper, AMHS productivity detractors affecting small lot manufacturing are studied, including the track layout, number of vehicles, empty vehicle management rules, number of stockers, stocker capacity, among others. Linked simulation models were developed for the 12-wafer-lot and the 25-wafer-lot systems, using AutoSched AP to simulate wafer processing and AutoMod to simulate the AMHS. The AMHS productivity detractors under study were varied for experimental purposes, and each scenario was quantitatively analyzed. Changes in the factory logistics of the 25-wafer-lot AMHS led to the development of the 12-wafer-lot AMHS, resulting in less congestion around high-throughput areas and faster AMHS delivery speeds. Simulation results showed improved AMHS performance despite the significant increase in the amount of wafer moves per hour caused by 12-wafer-lot manufacturing. The transition of semiconductor wafer fabrication plants (fabs) to small lot manufacturing (SLM) is the next step in the continuous improvement of chip manufacturing. Wafers are currently processed and moved in lots of 25 wafers per carrier, but SLM will use carriers with 12 wafers or less. Several studies have demonstrated that this waste-reduction solution will ultimately improve overall efficiency of production, and thus improve wafer cycle time (Bass and Wright 2008). In 12-wafer-lot manufacturing, the transport and storage requirements of the Automated Material Handling System (AMHS) will double in relation to the requirements of 25-wafer-lot manufacturing. Pillai (2006) suggested that high-speed, low variability AMHS will be needed to enable 12-wafer-lot systems. However, the AMHS is currently a productivity detractor of small lot size operations because existing transport technologies provide delivery speeds that are too low to maintain the increased move requirements. The AMHS also has high dependence on centralized storage systems, which leads to unnecessary congestion and increases the AMHS inefficiencies. With this in mind, the purpose of this paper is to configure the AMHS factors that limit the capacity of 12-wafer-lot systems, seeking to optimize the fab logistics and minimize traffic congestion around high-throughput areas of the fab. To accomplish this purpose, linked simulation models of a virtual 300mm fab were developed in AutoSched AP and AutoMod. These models study at a higher level of de-2575 978-1-4244-9864-2/10/$26.00 ©2010 IEEE
REF used integrated models to evaluate the impact of Small Lot Manufacturing (SML) and to test changes in the factory logic.
AMHS factors enabling small wafer lot manufacturing in semiconductor wafer fabs
WSC '10
Computer Science