Overlay and edge placement error metrology in the era of stochastics

For the most advanced nodes, edge placement errors are typically dominated by stochastics, necessitating a rigorous stochastics approach to modeling and measuring edge placement errors and their contributors. In this work, a new approach to developing an edge placement error (EPE) model useful for lot dispositioning or EPE budgeting is presented. Approach: As an example of the proposed approach, a rigorous EPE model is developed for the case of complementary lithography, where dense lines and spaces are cut with a second patterning step. This model gives rise to the generation of an Overlay Process Window, the range of overlay errors that can be tolerated in the presence of stochastics critical dimension and placement errors of the individual layers. The resulting model uses only measurable quantities and allows the prediction of EPE-based failure rates for the purpose of lot dispositioning. One interesting outcome is that Angstrom-level changes in the 1-sigma stochastics terms produces nanometer-level changes in the overlay process window. This new EPE modeling approach provides a more rigorous and accurate method for lot dispositioning and EPE budgeting than prior approaches.