AMHS factors enabling small wafer lot manufacturing in semiconductor wafer fabs

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.