A cluster tool for semiconductor manufacturing integrates several single wafer processing modules with a material handling system such as a robot. However, a new multi-slot tool architecture that processes several wafers simultaneouly at each processing module is recently proposed in order to maximize the throughput per the footprint. We examine steady state scheduling methods of a dual-armed multi-slot cluster tool. Two conventional scheduling methods, the swap strategy and the single-arm strategy, are examined for their performances for dual-armed multi-slot tools.
The swap strategy exchanges the wafer at an arm with the processed wafer at a module. It is known to be superior than any other scheduling method for dual-armed cluster tools. The single-armed strategy uses only a single arm as in a single-armed cluster tool. We show that in a dual-armed multi-slot tool, the single-arm strategy leads to the higher throughput rate than the swap strategy under some condition. We propose a new hybrid scheduling strategy that combines the merits of the two scheduling methods and analyze the performance.