Calibration-based overlay sensing with minimal-footprint targets

Overlay measurements are a critical part of modern semiconductor fabrication, but overlay targets have not scaled down in the way devices have. In this work, we produce overlay targets with very small footprint, consisting of just a few scattering nanoparticles in two separate device layers. Using moire patterns to deterministically generate many overlay errors on a single chip, we demonstrate readout of the relative displacement between the two layers and show that calibration on one realization of the targets can be used for overlay measurements on subsequent instances. Our results suggest that using greater quantities of smaller overlay targets may benefit performance both directly and through finer sampling of deformation.

Automated summary

The study produced very small overlay targets for accurately determining overlay errors and relative displacement between two separate device layers, which can be used for subsequent overlay measurements. Using greater quantities of smaller overlay targets could improve performance directly and provide finer sampling of deformation.