Broadband extreme ultraviolet zero-order Scatterometry for nanostructure metrology

The continuous shrinkage of the Critical Dimension in nanoscale fabrication demands new short-wavelength nanometrology approaches. Most industrial metrology is carried out on periodic structures to increase diffraction efficiencies and lower costs. Vice versa, performing short-wavelength spectroscopy on well-known structures allows reconstructing both amplitude and phase of reflected light, greatly increasing the information content of a measurement. Here, we introduce a table-top High-Harmonic Generation scatterometry approach operating in the extreme ultraviolet range. Our method exploits the typically overlooked 0-th diffraction order, which, despite lacking spatially encoded information, carries valuable spectrally encoded information and provides the highest diffraction efficiency. This approach constitutes a fast, reliable and non-destructive method for nanostructure metrology. Relative reflectivity measured in a grazing incidence reflection configuration goes beyond the need for an absolute calibration of the setup, and the morphology reconstruction protocol hereby presented makes this approach robust against fabrication imperfections. Rigorous Coupled-Wave Analysis simulations underpin a library-based inverse reconstruction approach, demonstrating precise determination of critical dimensions and groove heights on Silicon grating structures with nanometer-scale accuracy of 10 nm for critical dimension and 1 nm for groove height within 70% confidence intervals. Extreme-ultraviolet high-harmonic-generation based scatterometry leverages diffraction from structures with at-wavelength features and delivers sensitivities and accuracies to structural details far below the diffraction limit.