A new metrology technique for defect inspection via coherent Fourier scatterometry using orbital angular momentum beams

摘要

Coherent Fourier scatterometry (CFS) via laser beams with a Gaussian spatial profile is routinely used as an in-line inspection tool to detect defects on, for example, lithographic substrates, masks, reticles, and wafers. New metrology techniques that enable high-throughput, high-sensitivity, and in-line inspection are critically in need for next-generation high-volume manufacturing including those based on extreme ultraviolet (EUV) lithography. Here, a set of novel defect inspection techniques are proposed and investigated numerically [Wang et al., Opt. Express 29, 3342 (2021)], which are based on bright-field CFS using coherent beams that carry orbital angular momentum (OAM). One of our proposed methods, the differential OAM CFS, is particularly unique because it does not require a pre-established database for comparison in the case of regularly patterned structures with reflection symmetry such as 1D and 2D grating structures. We studied the performance of these metrology techniques on both amplitude and phase defects. We demonstrated their superior advantages, which shows up to an order of magnitude higher in signal-to-noise ratio over the conventional Gaussian beam CFS. These metrology techniques will enable higher sensitivity and robustness for in-line nanoscale defect inspection. In general, our concept could benefit EUV and x-ray scatterometry as well.