Matching between simulations and measurements as a key driver for reliable overlay target design

Numerical simulation of overlay metrology targets has become a de-facto standard in advanced technology nodes. While appropriate simulation software is widely available in the industry alongside with metrics that allow selection of the best performing targets, the model validation tools are less developed. We present an approach of numerical model validation based on the comparison between target simulation results and on-product overlay measurements. A "simulation-tomeasurement" software is used in this work to compare the performance metrics and accuracy flags of scatterometrybased overlay targets designed using KLA-Tencor AcuRate™ simulator for the critical layers of 12nm FD-SOI FEOL stack and 22nm FD-SOI BEOL stack. We demonstrate how simulation-to-measurement matching enabled us to verify the model, identify discrepancies between the model and the product stack and build an improved model that correctly describes the target. The refined target stack was used for image-based overlay target simulations that allowed us to obtain better performing optical overlay targets as well.