Antisymmetric structure detection using orthogonally polarized back-focal-plane imaging for deep-subwavelength targets.

In micro/nanofabrication for integrated circuits and metastructures, fabrication errors can break structural symmetry and degrade device performance. For deep-subwavelength periodic structures, the antisymmetric characteristics are typically weak and easily buried by the strong background signals. Here, we propose an antisymmetric structure detection method based on orthogonally polarized back-focal-plane (BFP) imaging by collecting the zeroth-order diffraction from a deep-subwavelength target. The method suppresses the strong symmetric background signals and isolates the antisymmetric component using the 180° rotation differencing. Simulations of nanometer-scale overlay show that the antisymmetric signal induced by overlay errors can be detected and extracted under noisy conditions.