Intra-field alignment for overlay feed-forward simulation with sampling optimization

It was proven that higher order intra-field alignment data modeling and correction has the potential to improve overlay performance by correcting reticle heating and lens heating effects intra-wafer and wafer- to-wafer.1 But there were also challenges shown that needed further investigation. As the alignment measurement is done on a coordinate system with absolute positions, the modeled iHOPC values might be high. A suitable method needs to be developed to distinguish between tool-to-tool offsets, process influence and layer-to-layer tool stack effect. In this paper we will take the next step and evaluate the overlay improvement potential by using intra-field alignment data in an overlay feed-forward simulation. An overlay run-to-run simulation is afterwards performed to estimate the optimization potential. To simulate higher order intra-field overlay, dense alignment data is needed. Facing the challenge of optimizing the number of measured marks but not losing relevant information, an intra-field alignment mark sampling optimization is done to find the best compromise between throughput and overlay accuracy.