A generic model for cluster tool throughput time and capacity

The throughput time within a cluster tool can be approximated as T+lt, where T is the fixed throughput time of the cluster, l is the lot size, and t is the average incremental throughput time resulting from a lot size increase of one wafer. Simulations of different cluster tools are used to illustrate and validate the model. The fixed throughput time (T) consists of both an external component associated with loadlock operations such as loading and pumping, and an internal component resulting from dynamic effects such as congestion in the cluster tool. The expressions for the incremental throughput time (t) includes the wafer handling time, and may include the module processing time. This model predicts that the maximum throughput rate of the cluster tool is 1/t, and that this throughput rate can only be achieved if multiple lots can simultaneously access the cluster tool. The model also predicts that this number of lots must increase, for example, as lot size decreases, the number of identical modules on a cluster increases, or lot loading time increases. This model was applied to a CVD cluster tool at Intel Corporation. The model predicted an increase in the cluster's throughput rate of roughly 10% over current operating practice, if one lot could be loaded while a different lot was being processed. The model was verified using a simulator and then on the cluster tool itself.