A tool portfolio planning methodology for semiconductor wafer fabs

Tool portfolio planning is a frequent task in semiconductor wafer fabrication plants, as process, machine and product technologies evolve rapidly and the plants go through capacity expansion. As wafer fabrication plants are complex integrated factories with conspicuous queuing effects phenomena, portfolio planning must take into consideration machine utilization, factory throughput, and total flow time simultaneously. This paper describes a tool portfolio planning methodology for wafer fabrication foundry plants. An improved static capacity model is first presented. A portfolio planning procedure based on static capacity estimation and queuing analysis is next described. A software implementation of the procedure is also used to clarify dilemmas of planning. It is shown that empirical formulas can be used to estimate the efficiency of batch machines. It is also used to show three types of portfolio adjustment action: flow time reduction, cost reduction and effectiveness improvement.