Research On The Final Transient State Of Dual-arm Cluster Tools With Wafer Revisiting

Wafer fabrication is the core of semiconductor manufacturing. With the increase of wafer size, the processing technology has become increasingly complicated. Therefore, automatic cluster tools are increasingly adopted in wafer fabrication. There is no buffer space in cluster tools except a robot, which makes its scheduling complicated. For some wafer fabrication processes, such as atomic layer deposition, require the wafers to visit some steps more than once, it is shown that the system is deadlock-prone. For dual-arm cluster tool with revisiting, the scheduling methods available are based on steady state. Wafer fabrication, however, contains three stages of processing including initial transient process, steady state and final transient process. Analysis and optimization of the final transient process is of great significance for the wafer processing trend of multi variety and small batch.Timed Petri nets have been widely used to deal with concurrent activities and the logical relationship of each process for discrete manufacturing systems, such as cluster tools. In this thesis, based on Petri net model of steady state and 1-wafer cyclic schedule of dual-arm cluster tools, the final transient process is analyzed by adopting the method of virtual wafer model. Furthermore, the final transient processing time in different conditions is found by using expressions.Based on 1-wafer cycle schedule, the scheduling of final transient process for dual-arm cluster tools is optimized by establishing a modified PN model. To reduce the processing time of final transient process, a new scheduling for dual-arm cluster tool involving the final transient process of an ALD process is presented. It shows the system can quickly switch to another group of wafer processing and the cycle time can be calculated by analytical expressions.Two simulation models of 1-wafer cyclic schedule and 1-wafer optimized schedule of final transient process for dual-arm cluster tool are established by Plant Simulation as a simulation platform, thus two kinds of scheduling for the final transient process simulation of machining process. Meanwhile, illustrative examples are given to obtain two groups processing time of the final transient process. Then compared with the processing time at identical conditions, it shows that 1-wafer optimized schedule can significantly improve the efficiency of wafer processing for the final transient process, thus verify the feasibility of scheduling and application of the results.Finally, the future study is presented.