Optimizing stepper mix to combat rising fab costs

A mix/match strategy using high throughput lower-cost noncritical steppers combined with more expensive critical layer steppers is an excellent way to combat escalating equipment costs and increase capital productivity as well as lower operating costs. To maximize capital productivity over a long term and ensure return on investment it is important to buy enough performance for several generations of devices, while still minimizing the price/throughput ratio. Convincing arguments in this paper present the strategy of using 5x compatible non-critical steppers with high performance to support a strategy of achieving multiple generations of design rules with one equipment set. In addition the 5x stepper has a favorable price/throughput ratio when compared with 5x critical steppers. Finally, for fab managers, the practical logistics of manufacturing operations favors a choice of 5x compatibility when the issues of stepper capacity utilization, reticle compatibility, operator training, engineering process knowledge, spare parts and service engineering are considered.