Research On Real-time Dispatching Methods In Semiconductor Manufacturing Automated Material Handling Systems

Semiconductor Wafer Fabrication System(SWFS)is one of the most complicate discrete processing systems,which is different from traditional flow-shop and job-shop manufacturing systems.SWFS has distinguished characteristics such as reentrancy,mass and mixed products in processing,sophisticated processing operations,long fabrication cycle time,high capital investment and uneven load on equipments,etc.With the development of science and technology,wafer size and weight has increased.The workload of wafer handling also increases and has pushed the traditional manual material handling to its limits.Thus the Automated Material Handling System(AMHS)has been widely adopted by the semiconductor manufacturing fab in all over the world,The efficient operation of AMHS has a critical role in improving production efficiency and gaining economic benefit in SWFS.How to dispatch efficiency of AMHS has become a critical and urgent problem to be solved.AMHS includes the Interbay and Intrabay material handling system,and the Interbay system is the most important sub-system.We developed a simulation model,better reflect the real FAB: considered the the unreliability of the equipments,fully considered the workloads of every bay,especially the bottleneck Bay’s workload impact on AMHS performance,each Stocker has a limited capacity and separates input Buffer from the output Buffer,considered the turntable time and grab time.Through the Interbay optimal scheduling,we can reduce wafer lot’s waiting time,shorten the cycle time,low the Work In Process(WIP),promote the vehicle efficiency and increase throughput of wafers,etc.Therefore,the research on the optimal scheduling methods of Interbay automated material handling system has great significance to the promotion of SWFS.The detailed research contents of this thesis are as follows.(1)According to the distinguished characters of the scheduling of 300 mm semiconductor wafer Interbay AMHS,aiming to reduce the transfer time and promote the overall AMHS performance.A cost model of dispatching is proposed considering multiple factors in real time dispatching.Hungarian algorithm based dispatching strategy is then presented to solve the real-time optimal dispatching problem.(2)As the Interbay AMHS status is changing in real-time and stochastic.We proposed a dynamic weights of multi-objective cost model based on fuzzy logic,which can change the weight of each perfomance indice if the system status changes.Based on the dynamic weights of multi-objective cost model,we analysis the sensitively of the fuzzy rules,modified and expanded the fuzzy rules from the previous studies.(3)Developed a 300 mm Interbay AMHS simulation model based on simulation software Arena,then based the VBA interface for secondary development.This simulation model included 24 subsystem Intrabays and more sophisticated processing operations and high rate of reentrancy.At last,we code the dispatching rules proposed in this thesis and integrated the VB code into the AMHS simulation model based on Arena VBA to validate the effectiveness of the proposed real-time multi-objective dispatching method.The experiments suggest the proposed approach outperforms traditional dispatching rules in performance indices,such as cycle time,throughput,vehicle utilization,vehicle movement and work in process.The experiment results of this thesis provide some novel methods and expand some theory for the complicated semiconductor AMHS,which have important theoretical and practical significance to the real FAB.