Scheduling And Buffering Space Configuration For Multi-cluster Tools With Tree-like Topology

In semiconductor manufacturing,wafer fabrication is a very complicated process,so cluster tool is widely used in wafer processing to ensure production quality and precision.As a highly automated and integrated manufacturing system,a single-cluster tool usually includes 4-6 wafer processing modules,one wafer handling robot and two loadlocks for wafer cassette loading/unloading.Because the price of the processing equipment is extremely high and scheduling a cluster tool is a NP-hard problem,it is urgent to optimize the operation and effective control of the equipment,so as to improve the utilization ratio of the equipment.With the increasing requirement of wafer processing,multi-cluster tools have gradually become the choice of the semiconductor manufacturing enterprises.It is a manufacturing system composed of a number of single-cluster tools.The single-cluster tool is connected by a buffer module to each other and forms two different topological structures of linear and tree-like topology.For the multi-cluster tools scheduling,the key is the interactions between each single cluster tool,processing time fluctuation of any equipment will form a cumulative effect in the whole system,so that the synchronization of robots is difficult to achieve.Therefore,in multi-cluster tools scheduling,it is very important to solve the synchronization of the coordination of robot in the buffering module.In the previous studies,the single-cluster tool scheduling has been relatively mature,but there are still many problems to be solved in multi-cluster tools scheduling.Resently,lots of researches have been conducted on linear multi-cluster tools,considering the complexity of multi-cluster tools with tree-like topology,how to schedule the system is still a problem to be further studied.This paper is focus on a single-arm tree-like multi-cluster tools with two-space buffering modules.When the moving time of the multi-cluster tools is much less than that of the wafer processing,the processing cycle of the system is determined by the wafer processing time,and there is an idle waiting time for the robot.The first problem solved in this paper is whether there is one-wafer optimal cyclic schedule,and how to obtain the optimal scheduling;At the same time,because of the extremely high price of cluster tool,the redundant buffering space will become the cost of enterprises,therefore,after scheduling the system with two-space buffering modules,this thesis discuss how to optimal the buffering space structure in order to reduce the use of buffer module.To solve the problems above,resource-oriented Petri net has been used to set up a model which can accurately describe the three stages of the system with two-space buffering modules: initial transient state,stable state and terminal transient state.Based on the Petri net model,conditions are presented under which a one-wafer cyclic schedule with the lower bound of cycle time can always be found and an algorithm is developed to coordinate the activities of adjacent arms,then the effectiveness and practicability of the algorithm is verified by an example;This paper uses Petri net to rebuilt the describing model to solve the problem of optimizing the space of the buffering modules because the system has different structure and operation process.The colors have been introduced into the Petri net model to solve the deadlock caused by resource sharing in buffering modules.With this new model,the optimality and schedulability of the system has been analyzed when there is different space capacity in buffering module.By cutting the tree-like multi-cluster tools into several linear cluster tool chain,an algorithm is given to obtain the schedule optimizing the buffering spaces.Finally,illustrative example is presented to verified the effectiveness of algorithm.