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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. [ABSTRACT FROM AUTHOR]

Large-scale sports are often held in large cities with heavy traffic, which makes it difficult to satisfy the transportation requirement. To solve this problem, lane reservation method is often adopted. However, it may make the host city's own transportation even worse. Therefore, it is necessary to study how to make lane reservation. While previous studies mainly focus on minimizing the effect on regular transportation, the present study also discusses the possibility of reducing the number of transporting vehicles. By evaluating in advance, some transport tasks can be merged. Accordingly, the number of transport vehicles is cut down and operation cost is reduced. Based on this, a linear integer programming model is formulated. The model is different from the existing models with transportation network, constraint of task path, constraint and measure of making reservation lane. It is shown that the problem is NP-hard. It can be solved by exact methods if it is not too large. The model is proved to be valid and practical by the results shown by Lingo, a Mathematical programming software as in the example of Guangzhou Asia Games. [ABSTRACT FROM AUTHOR]

With wafer residency time constraint and activity time variation, it is very difficult to schedule a cluster tool and to check if a given schedule is feasible. To solve this problem, simulation can be used to determine if a given schedule is feasible and help to obtain a feasible schedule. For this purpose, in this paper a virtual single-arm cluster tool is developed by using eM-Plant simulation system. A cluster tool is reconfigurable and can be used to process different types of wafers. Different type of wafers has different flow pattern and different processing times. Thus, the virtual cluster tool should be reusable. With parmneterization, the system is made to be reusable. It is a 3-dimention model so that it is visualized. Thus, it is useful for practitioners to operate a cluster tool. Examples are presented to demonstrate the applications of the system. [ABSTRACT FROM AUTHOR]

Because of residency time constraints and activity time variation of cluster tools, it is very difficult to operate such integrated semiconductor manufacturing equipment. This paper addresses their real-time operational issues. To characterize their schedulability and achieve the minimum cycle time at their steady-state operation, Petri net (PN) models are developed to describe them, which are very compact, and independent of wafer flow pattern. It is due to the proposed models that scheduling cluster tools is converted into determining robot wait times. A two-level operational architecture is proposed to include an offline periodic schedule and real-time controller. The former determines when a wafer should be placed into a process module for processing, while the latter regulates robot wait times online in order to reduce the effect of activity time variation on wafer sojourn times in process modules. Therefore, the system can adapt to activity time variation. A cluster tool derived as a not-always-schedulable system by the existing methods is shown to be always-schedulable by using the proposed novel method. [ABSTRACT FROM PUBLISHER]