Systems of multiple cluster tools: configuration and performance under perfect reliability

By extrapolating technological trends, one can expect future fabs to consist largely of highly reliable cluster tools. Such trends raise the issues of how cluster tools should be configured (i.e., how modules should be grouped together), and the impact of configuration on optimal lot size. This paper generates equation-based models to compare the throughput and cycle time of different systems that perform the same sequence of process steps, with the same total number of modules grouped in different ways into multiple cluster tools. The two extremes of the spectrum of possible cluster tool configurations are considered: the serial configuration, in which a wafer visits each module in the cluster tool, and the parallel configuration, in which all of the modules in the cluster tool are identical. The models predict the following for typical cluster tool parameters and process times. When all process step times are identical, systems of serial-configured tools can achieve the same throughputs with lower cycle times, as their parallel-configured counterparts. However, if process times in the sequence significantly differ from one another, then systems of parallel-configured tools may achieve lower cycle times than their serial-configured counterparts at high throughputs. Finally, the serial configuration significantly reduces the lot size required to achieve total throughput capacity.