Sampling strategy: optimization and correction for high-order overlay control for 45nm process node

The tight overlay budgets required for 45nm and beyond make overlay control a very important topic. With the adoption of immersion lithography, the incremental complexity brings much more difficulty to analyzing the source of variation and optimizing the sampling strategy. In this paper, there will be a discussion about how the use of an advanced sampling methodology and strategy can help to overcome this overlay control problem and insure sufficient overlay information to be captured for effective production lot excursion detection as well as rework decision making. There will also be a demonstration of the different correction methodologies to improve overlay control for dual-stage systems in order to maximize the productivity benef its with minimal impact to overlay performance.