Calibration-based overlay sensing with minimal-footprint targets

Abstract

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 moiré patterns to deterministically generate many overlay errors on a single chip, we demonstrate successful 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 using greater quantities of smaller overlay targets may benefit performance both directly and through finer sampling of deformation.