Characterization of nanoscale gratings by spectroscopic reflectometry in the extreme ultraviolet with a stand-alone setup

The authors present a study on the dimensional characterization of nanoscale line gratings by spectroscopic reflectometry in the extreme ultraviolet spectral range (5 nm to 20 nm wavelength). The investigated grating parameters include the line height, the line width, the sidewall angle and corner radii. The study demonstrates that the utilization of shorter wavelengths in state-of-the-art optical scatterometry provides a high sensitivity with respect to the geometrical dimensions of nanoscale gratings. Measurable contrasts are demonstrated for dimensional variations in the sub-percent regime, down to one tenth of a nanometer and one tenth of a degree in absolute terms. In an experimental validation of the method, it is shown that reflectance curves can be obtained in a stand-alone setup using the broadband emission of a discharge produced plasma as the source of EUV radiation, demonstrating the potential scalability of the method for industrial uses. Simulated reflectance curves are fit to the experimental curves by variation of the grating parameters using rigorous electromagnetic modeling. The obtained grating parameters are cross-checked by a scanning electron microscopy analysis.