Limits of detection of defects near edges of nanostructures for coherent Fourier scatterometry

Abstract

Coherent Fourier scatterometry (CFS) is a non-invasive optical technique widely used for defect detection on planar surfaces. It utilizes split detectors to measure far-field asymmetries as differential signals, making it highly effective for identifying defects such as particles or burrows. Detecting defects near edges of nanostructures, however, is particularly challenging due to interference between the edge signal and the defect signal, a limitation not only of CFS but also of other standard techniques like bright-field and dark-field microscopy. Accurate detection of such defects is critical in fields like semiconductor manufacturing and nanotechnology, where edge-adjacent defects can compromise device performance. Therefore, understanding the limits of CFS for edge-adjacent defect detection is essential for optimizing its application and interpreting its results. In this work, we first demonstrate experimentally that CFS can detect a 200 nm Pt particle positioned 2 µm from an edge. We then perform 3D FDTD simulations to model particles and burrows positioned at varying distances from an edge. By analyzing the split detector signals for these scenarios, we observe that particle and burrow signals become more prominent as their distance from the edge increases. However, for a system using a numerical aperture of 0.9 and wavelength of 633 nm, for distances from the edge smaller than 350 nm for particles and 650 nm for burrows, the characteristic signals diminish, merging with the edge response. This study highlights the challenges and potential solutions for defect inspection near edges, advancing the applicability of CFS for patterned and complex structures.