Economic Assessment of Lithography Strategies for the 22nm Technology Node

摘要

The unavailability of extreme ultra violet lithography (EUVL) for mass production of the 22nm technology node has created a significant void for mainstream lithography solutions. To fill this void, alternate lithography solutions that were earlier deemed to be technically and economically infeasible, such as double patterning technologies (DPT), source mask optimization (SMO), massively parallel direct write e-beam (MEBM) and Interference assisted lithography (Intf), are being proposed, developed and adopted to ensure the timely deployment of the 22nm technology node. While several studies have been undertaken to estimate the lithography process costs for volume production with the aforementioned technologies, these studies have provided only a partial analysis since they have not taken into account the impact on design density and product yield.In this paper we use the cost-per-good-die metric in order to capture process costs as well as yield and design density. We have developed a framework that estimates the lithography cost-per-good-die for SRAM arrays and have applied it to evaluate the economical feasibility of the various lithography strategies under consideration for the 22nm technology node. Specifically, we compare the cost-per-good-die for different 32MB SRAM arrays, each optimized for a different lithography solution. Our analysis shows that the selection of the best lithography strategy is both layer and volume specific. The use of DPT solutions is recommended for Active and Contact layers. The use of Intf is recommended for layers such as Poly, Metals and Vias in the case of low volume products. For medium to high volume products the use of SMO is recommended for Poly, Metals and Vias. This paper provides quantifies of economic benefit of the proposed lithography strategy.