Overlay metrology performance prediction fidelity: the factors enabling a successful target design cycle

Overlay metrology performances highly depend on the detailed design of the measured target. Hence performing simulations is an essential tool for optimizing target design. We demonstrate for scatterometry overlay (SCOL) three key factors which enable consistency in ranking between simulated and measured metrology performance for target design. The first factor, to enable high fidelity simulations for the purpose of target design, is stack and topography verification of model inputs. We report in detail the best known film metrology methods required to achieve model integrity. The second factor is the method of calculation of metrology performance metrics based on target cell reflectivities from electro-magnetic (EM) simulations. These metrics enable ranking of different designs, and subsequent choice of the best performing designs among all simulated design options, the ranking methodology being the third factor. We apply the above steps to a specific stack, where five different designs have been considered. Simulated versus measured values are compared. A good agreement between simulation and measurement is achieved.