Determining the shape and periodicity of nanostructures using small-angle X-ray scattering

TLDR

The semiconductor industry seeks metrology capable of characterizing sub‑10‑nm 3D structures, and small‑angle X‑ray scattering, particularly CDSAXS, offers sub‑Å wavelength sensitivity that can determine the average shape of line gratings. The authors applied CDSAXS to line gratings produced by self‑aligned multiple patterning, varied line spacing by sub‑nm shifts, and modeled the scattering with progressively complex simulations to justify the numerous parameters. Model comparisons show the technique resolves shape differences within the superlattice and measures line shape and spacing to sub‑nm precision, confirming CDSAXS as a high‑resolution nanostructure metrology tool.

Abstract

The semiconductor industry is exploring new metrology techniques capable of meeting the future requirement to characterize three-dimensional structure where the critical dimensions are less than 10 nm. X-ray scattering techniques are one candidate owing to the sub-Å wavelengths which are sensitive to internal changes in electron density. Critical-dimension small-angle X-ray scattering (CDSAXS) has been shown to be capable of determining the average shape of a line grating. Here it is used to study a set of line gratings patterned via a self-aligned multiple patterning process, which resulted in a set of mirrored lines, where the individual line shapes were asymmetric. The spacing between lines was systematically varied by sub-nm shifts. The model used to simulate the scattering was developed in stages of increasing complexity in order to justify the large number of parameters included. Comparisons between the models at different stages of development demonstrate that the measurement can determine differences in line shapes within the superlattice. The shape and spacing between lines within a given set were determined to sub-nm accuracy. This demonstrates the potential for CDSAXS as a high-resolution nanostructure metrology tool.