Table-top HHG EUV scatterometry for roughness and structural parameters evaluation in nano-stacks

Extreme ultraviolet (EUV) or soft X-ray scatterometry is a powerful technique enabling contactless non-destructive structural characterization of patterned nano-stacks with down to sub-nanometer precision1. The technique requires coherent EUV / soft X-ray radiation and is thus typically limited to a synchrotron or free-electron laser facilities. With the continual improvement of table-top high-harmonic-generation (HHG) sources over the last few decades, this approach has become feasible in a lab-scale environment. Here we present EUV scatteromertric results obtained using the coherent 92 eV HHG source in imec’s AttoLab on grating-type samples highly relevant for semiconductor industry. Roughness characterization was performed via direct detection of scattered light utilizing a synthetic aperture and high-dynamic-range detection coupled with noise suppression techniques. Structural parameters (CD, pitch, height, angles, layer and interlayer diffusion thicknesses) were obtained by fitting the sample model to match simulated diffraction patterns to the experimental ones. The latter were acquired through a wide angular scanning (ranging 0 to 65° from grazing). The simulated patterns were calculated by propagating light (using JCMsuite software) through a model of the structured sample. The results demonstrate sub-nanometer precision and are in good agreement with AFM and TEM measurements.