Scheduling and analysis of start-up transient processes for dual-arm cluster tools with wafer revisiting

The trends of increasing wafer diameter and smaller lot sizes have led to more transient periods in wafer fabrication. For some wafer fabrication processes, such as atomic layer deposition, wafers need to visit some process modules for a number of times, instead of once, thus leading to a so-called revisiting process. Most previous studies on cluster tool scheduling focus on steady state at which cluster tools repeat identical cycles. Research on transient processes of dual-arm cluster tools with wafer revisiting processes becomes urgently needed for high-performance wafer fabrication. In order to speed up start-up transient processes, this paper adopts a program evaluation and review technique for the analysis of start-up transient processes and develops optimization algorithms for their scheduling of dual-arm cluster tools. Then, their complexity is analyzed. Finally, illustrative examples are given to show the applications of the proposed method.